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Document and Entity Information - shares	3 Months Ended
Mar. 31, 2018	Apr. 25, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Trading Symbol	NBIX
Entity Registrant Name	NEUROCRINE BIOSCIENCES INC
Entity Central Index Key	0000914475
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		89,897,863

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 175,311	$ 254,712
Short-term investments, available for sale	285,168	261,217
Accounts receivable, net	44,624	31,127
Other current assets	8,613	7,863
Total current assets	513,716	554,919
Property and equipment, net	11,825	10,811
Long-term investments, available for sale	276,319	247,361
Restricted cash	4,500	4,500
Total assets	806,360	817,591
Current liabilities:
Accounts payable and accrued liabilities	45,650	53,520
Current portion of cease-use liability		62
Current portion of deferred gain on sale of real estate	731	731
Other current liabilities	85	113
Total current liabilities	46,466	54,426
Deferred gain on sale of real estate	7,860	8,043
Deferred revenue	10,231	10,231
Deferred rent	3,107	3,135
Convertible senior notes	374,209	369,618
Total liabilities	441,873	445,453
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.001 par value; 220,000,000 shares authorized; issued and outstanding shares were 89,882,062 as of March 31, 2018 and 88,793,903 as of December 31, 2017	90	89
Additional paid-in capital	1,608,778	1,572,765
Accumulated other comprehensive loss	(3,697)	(1,850)
Accumulated deficit	(1,240,684)	(1,198,866)
Total stockholders’ equity	364,487	372,138
Total liabilities and stockholders’ equity	$ 806,360	$ 817,591

Condensed Consolidated Statements of Operations And Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Product sales, net	$ 71,086	$ 0
Total revenues	71,086	0
Operating expenses:
Cost of product sales	950	0
Research and development	48,947	51,882
Sales, general and administrative	58,636	28,050
Total operating expenses	108,533	79,932
Loss from operations	(37,447)	(79,932)
Other (expense) income:
Deferred gain on real estate	201	879
Interest expense	(7,504)	0
Investment income, net	2,932	727
Total other (expense) income	(4,371)	1,606
Net loss	$ (41,818)	$ (78,326)
Net loss per common share:
Basic and diluted	$ (0.47)	$ (0.90)
Shares used in the calculation of net loss per common share:
Basic and diluted	89,526	87,283
Other comprehensive loss:
Net loss	$ (41,818)	$ (78,326)
Net unrealized (losses) gains on available-for-sale securities	(1,847)	83
Comprehensive loss	$ (43,665)	$ (78,243)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (41,818)	$ (78,326)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	786	489
Gain on sale of assets, net	(201)	(879)
Amortization of debt issuance costs	326	0
Amortization of debt discount	4,265	0
Deferred rent	(28)	(114)
Amortization of premiums on investments	512	269
Non-cash share-based compensation expense	19,879	8,976
Change in operating assets and liabilities:
Accounts receivable	(13,497)	(779)
Other current assets	(750)	0
Accounts payable and accrued liabilities	(7,870)	(6,927)
Cease-use liability	(62)	(66)
Other liabilities	(28)	0
Net cash used in operating activities	(38,486)	(77,357)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of investments	(139,354)	(57,877)
Sales and maturities of investments	84,086	116,085
Proceeds from sales of property and equipment	18	0
Purchases of property and equipment	(1,800)	(1,362)
Net cash (used in) provided by investing activities	(57,050)	56,846
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of common stock	16,135	1,531
Net cash provided by financing activities	16,135	1,531
Net decrease in cash, cash equivalents and restricted cash	(79,401)	(18,980)
Cash, cash equivalents and restricted cash at beginning of the period	259,212	88,150
Cash, cash equivalents and restricted cash at end of the period	$ 179,811	$ 69,170

ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES	Mar. 31, 2018
Accounting Policies [Abstract]
ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES	1. ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES Description of Business. Neurocrine Biosciences, Inc. (the Company or Neurocrine) was incorporated in California in 1992 and reincorporated in Delaware in 1996. The Company discovers, develops and commercializes innovative and life-changing pharmaceuticals, in diseases with high unmet medical needs, through its novel research and development (R&D) platform, focused on neurological and endocrine based diseases and disorders. In April 2017, the Company received approval from the United States Food and Drug Administration (FDA) for INGREZZA^® (valbenazine), a vesicular monoamine transporter 2 (VMAT2) inhibitor for the treatment of tardive dyskinesia. The Company’s three lead late-stage clinical programs are elagolix, a gonadotropin-releasing hormone (GnRH) antagonist for women’s health that is partnered with AbbVie Inc. (AbbVie), INGREZZA for Tourette syndrome, and opicapone, a highly-selective catechol-O-methyltransferase inhibitor for the treatment of Parkinson’s disease. Basis of Presentation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (GAAP) for interim financial information and with the instructions of the Securities and Exchange Commission (SEC) on Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for complete financial statements. In the opinion of management, the condensed consolidated financial statements include all adjustments necessary, which are of a normal and recurring nature, for the fair presentation of the Company’s financial position and of the results of operations and cash flows for the periods presented. The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. These financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2017 included in the Company’s Annual Report on Form 10-K filed with the SEC. The results of operations for the interim period shown in this report are not necessarily indicative of the results that may be expected for any other interim period or for the full year. The balance sheet at December 31, 2017 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. Impact of Recently Issued Accounting Standards. In May 2014 the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. This new standard amends the guidance for the recognition of revenue from contracts with customers to transfer goods and services. The FASB subsequently issued additional, clarifying standards to address issues arising from implementation of the new revenue recognition standard. The Company adopted this new standard as of January 1, 2018 using the modified retrospective method. The adoption of the new revenue standards did not change the Company’s revenue recognition. As the Company did not identify any accounting changes that impacted the amount of reported revenues with respect to product revenues, or revenue from collaboration and license agreements, no adjustment to retained earnings was required upon adoption. See below for discussion of the Company’s Revenue Recognition policy. In February 2016, the FASB issued ASU 2016-02 Leases. This update amends the current accounting guidance for lease transactions. Under the new guidance, a lessee will be required to recognize both assets and liabilities for any leases in excess of twelve months. Additionally, certain qualitative and quantitative disclosures will also be required in the financial statements. The Company is required to adopt this new guidance beginning in 2019 and early adoption is permitted. The Company’s lease for its corporate headquarters is subject to this new guidance and the Company is in the process of determining the impact of the adoption of this update will have on its condensed consolidated financial statements is ongoing. In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash”, which clarifies the presentation of restricted cash and restricted cash equivalents in the statements of cash flows. Under this ASU, restricted cash and restricted cash equivalents are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts presented on the statements of cash flows. This ASU is intended to reduce diversity in practice in the classification and presentation of changes in restricted cash on the statement of cash flows. This ASU requires that the statement of cash flows explain the change in total cash and equivalents and amounts generally described as restricted cash or restricted cash equivalents when reconciling the beginning-of-period and end-of-period total amounts. This ASU also requires a reconciliation between the total of cash and equivalents and restricted cash presented on the statement of cash flows and the cash and equivalents balance presented on the balance sheet. This amended guidance was retrospectively adopted on January 1, 2018 and required that cash, cash equivalents and restricted cash reported on the Condensed Consolidated Statements of Cash Flows now includes restricted cash of $4.5 million and $5.1 million as of March 31, 2018 and 2017, respectively, as well as previously reported cash and cash equivalents. Use of Estimates. The preparation of the condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and the accompanying notes. Actual results could differ from those estimates. Inventory. Inventory is stated at the lower of cost or estimated net realizable value. The Company currently uses actual costing to determine the cost basis for its inventory. Inventory is valued on a first-in, first-out basis and consists primarily of third-party manufacturing costs. The Company capitalizes inventory costs associated with its products upon regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed. Prior to FDA approval of INGREZZA, all costs related to its manufacturing were charged to research and development expense in the period incurred. At March 31, 2018 and December 31, 2017, the Company’s physical inventory included active pharmaceutical product (API) that had been produced prior to FDA approval of INGREZZA and accordingly has no cost basis as the cost associated with producing this material was expensed rather than capitalized in accordance with authoritative guidance. Additionally, manufacturing of bulk drug product, finished bottling and other labeling activities that occurred post FDA approval are included in the inventory value at March 31, 2018 and December 31, 2017. The Company provides reserves for potential excess, dated or obsolete inventory based on an analysis of forecasted demand compared to quantities on hand and any firm purchase orders, as well as product shelf life. To date, the Company has determined that such reserves are not required. Cost of Product Sales. Cost of product sales consists of third-party manufacturing costs, transportation and freight, and indirect overhead costs associated with the manufacture and distribution of INGREZZA. Cost of product sales may also include period costs related to certain inventory manufacturing services, inventory adjustment charges as well as manufacturing variances. A significant portion of the cost of producing the product sold to date was expensed as R&D prior to the Company’s New Drug Application (NDA) approval for INGREZZA and therefore is not included in the cost of product sales during this period. Accounts Receivable. Accounts receivable are recorded net of customer allowances for prompt payment discounts, chargebacks, and any allowance for doubtful accounts. The Company estimates the allowance for doubtful accounts based on existing contractual payment terms, actual payment patterns of its customers and individual customer circumstances. To date, the Company has determined that an allowance for doubtful accounts is not required. Research and Development Expenses. R&D expenses consist primarily of salaries, payroll taxes, employee benefits, and share-based compensation charges, for those individuals involved in ongoing R&D efforts; as well as scientific contractor fees, development milestones from in-licensed collaboration agreements, preclinical and clinical trial costs, R&D facilities costs, laboratory supply costs, and depreciation of scientific equipment. All such costs are charged to R&D expense as incurred. These expenses result from the Company’s independent R&D efforts as well as efforts associated with collaborations and in-licensing arrangements. In addition, the Company funds R&D at other companies and research institutions under agreements, which are generally cancelable. The Company reviews and accrues clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of patient studies and other events. The Company follows this method since reasonably dependable estimates of the costs applicable to various stages of a research agreement or clinical trial can be made. Accrued clinical costs are subject to revisions as trials progress. Revisions are charged to expense in the period in which the facts that give rise to the revision become known. Revenue Recognition. Effective January 1, 2018, the Company adopted Topic 606, using the modified retrospective method, which it elected to apply to all contracts. As the Company did not identify any revenue recognition differences when comparing the revenue recognition criteria under Topic 606 to the requirements under previous criteria with respect to product revenues, or revenue from collaboration and license agreements, no cumulative effect adjustment to retained earnings was necessary upon adoption. See the Company’s Annual Report on Form 10-K filed with the SEC for the year ended December 31, 2017 for a detailed description of the Company’s accounting policy under Topic 605 which was effective for periods prior to January 1, 2018. The Company’s revenues for the first quarter of 2018, had the Company continued to account for revenue recognition under Topic 605, would not have differed by a significant amount from those reported under Topic 606. Under Topic 606, the Company recognizes revenues when its customers obtain control of its products or services in an amount that reflects the consideration it expects to receive from its customers in exchange for those products or services. To determine revenue recognition, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies the performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. If the consideration promised under the contract includes a variable amount, the Company must estimate the consideration it expects to receive for transferring the good or service to the customer. There are two methods for determining the amount of variable consideration: (i) the expected value method, which is the sum of probability-weighted amounts in a range of possible consideration amounts, and; (ii) the mostly likely amount method, which identifies the single most likely amount in a range of possible consideration amounts. Performance milestone payments represent a form of variable consideration. Product Sales, Net. The Company’s product sales consist of U.S. sales of INGREZZA. INGREZZA was approved by the FDA on April 11, 2017 and the Company commenced shipments of INGREZZA to select pharmacies (SPs) and a select distributor (SD), or collectively, its customers, in late April 2017. The SPs dispense product to a patient based on the fulfillment of a prescription and the SD sells product to government facilities, long-term care pharmacies or in-patient hospital pharmacies. The Company’s agreements with the SPs and SD provide for transfer of title to the product at the time the product is delivered to the SP or SD. In addition, except for limited circumstances, the SPs and SDs have no right of product return to the Company. Product sales are recognized when the customer obtains control of the Company’s product, typically upon delivery to the customer. Revenue from product sales are recorded at the net sales price (transaction price), which includes an estimate of variable consideration for which reserves are established and which results from contractual discounts, returns, chargebacks, rebates, co-pay assistance and other allowances relating to the Company’s sales of its products. These reserves are based on the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if the amount is payable to the customer) or a current liability (if the amount is payable to a party other than a customer). Where appropriate, these estimates take into consideration a range of possible outcomes that are probability-weighted for relevant factors such as the Company’s historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained, and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. The following are the Company’s significant categories of sales discounts and allowances: Trade Discounts and Allowances: The Company generally provides customers with discounts that include prompt payment discounts, discounts for providing sales data, and other off-invoice discounts that are explicitly stated in the Company’s contracts and are recorded as a reduction of revenue in the period the related product revenue is recognized. Product Returns: The Company offers customers limited product return rights for damages and shipment errors provided it is within a very limited period after the original shipping date as set forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient or for drug expiration. The Company receives real-time shipping reports and inventory reports from the customers and has the ability to control the amount of product that is sold to the customers. Product returns to date have not been significant and the Company has not considered it necessary to record a reserve for product returns. Government Rebates: The Company is subject to discount obligations under state Medicaid programs and Medicare prescription drug coverage gap program. The Company estimates its Medicaid and Medicare prescription drug coverage gap rebates based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability that is included in accrued expenses on the condensed consolidated balance sheet. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. Provider Chargebacks and Discounts: Chargebacks for fees and discounts to providers represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to customers who directly purchase the product from the Company. Customers charge the Company for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. These reserves are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider by customers, and the Company generally issues credits for such amounts following the customer’s notification to the Company of the resale. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at each reporting period end that the Company expects will be sold to qualified healthcare providers. Co-Payment Assistance: The Company offers co-payment assistance to commercially insured patients meeting certain eligibility requirements. The calculation of the accrual for co-pay assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. Shipping and handling costs related to the Company’s product sales are included in selling, general and administrative expenses. Collaborative Research and Development Agreements The Company enters into collaboration and licensing agreements that are within the scope of Topic 606, under which it licenses certain rights to its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services; and royalties on net sales of licensed products. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success. Licenses of Intellectual Property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, commercialization and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect milestone and license fees revenues and earnings in the period of adjustment. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its out-licensing arrangements. The Company receives payments from its licensees based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.

SIGNIFICANT COLLABORATIVE RESEARCH AND DEVELOPMENT AGREEMENTS	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
SIGNIFICANT COLLABORATIVE RESEARCH AND DEVELOPMENT AGREEMENTS	2. SIGNIFICANT COLLABORATIVE RESEARCH AND DEVELOPMENT AGREEMENTS Mitsubishi Tanabe Pharma Corporation (Mitsubishi Tanabe). During 2015, the Company entered into a collaboration and license agreement with Mitsubishi Tanabe for the development and commercialization of INGREZZA for movement disorders in Japan and other select Asian markets. Mitsubishi Tanabe made an up-front license fee of $30 million and has agreed to make payments up to $85 million in development and commercialization event-based payments, payments for the manufacture of pharmaceutical products, and royalties on product sales in select territories in Asia. Under the terms of the agreement, Mitsubishi Tanabe is responsible for all third-party development, marketing and commercialization costs in Japan and other select Asian markets. The Company will be entitled to a percentage of sales of INGREZZA in Japan and other select Asian markets for the longer of ten years or the life of the related patent rights. Under the terms of the Company’s agreement with Mitsubishi Tanabe, the collaboration effort between the parties to advance INGREZZA towards commercialization in Japan and other select Asian markets is governed by a joint steering committee and joint development committee with representatives from both the Company and Mitsubishi Tanabe. There are no performance, cancellation, termination or refund provisions in the agreement that would have a material financial consequence to the Company. The Company does not directly control when event-based payments will be achieved or when royalty payments will begin. Mitsubishi Tanabe may terminate the agreement at its discretion upon 180 days’ written notice to the Company. In such event, all INGREZZA product rights for Japan and other select Asian markets would revert to the Company. The Company assessed this arrangement in accordance with Topic 606 and identified the following material promises under the agreement: (i) INGREZZA technology license and existing know-how; and (ii) development activities to initiate a clinical trial of INGREZZA for Huntington’s chorea, at an estimated cost of approximately $12 million, should Mitsubishi Tanabe request. The Company has the option to participate on the joint steering committee, but since participation is at the Company’s option it was deemed to not be a material promise. The option for Mitsubishi Tanabe to engage the Company to manufacture and supply pharmaceutical products, not at a discount, was not considered a material right and therefore not a material promise. Based on these assessments, the Company identified the license and the development activities as the only performance obligations at the inception of the agreement, which were both deemed to be distinct. Under the terms of the agreement, in order to evaluate the appropriate transaction price, the Company determined that the up-front amount constituted the entirety of the consideration to be included in the transaction price and to be allocated to the performance obligations based on the Company’s best estimate of their relative stand-alone selling prices. For the license, the stand-alone selling price was calculated using an income approach model and included the following key assumptions: the development timeline, revenue forecast, discount rate and probabilities of technical and regulatory success. The relative selling price of the Company’s development activities to initiate a clinical trial of INGREZZA for Huntington’s chorea was based on an assessment of costs to perform the study, based upon the peer company analysis for similar studies. The Company believes that a change in the assumptions used to determine its stand-alone selling price for the license most likely would not have a significant effect on the allocation of consideration received (or receivable) to the performance obligations. At execution, the transaction price included only the $30 million up-front consideration received. None of the development or regulatory milestones has been included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to Mitsubishi Tanabe and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. To date, the Company has recognized revenue under this agreement of $19.8 million associated with the delivery of a technology license and existing know-how, and $15 million in development event-based payments resulting from Mitsubishi Tanabe’s initiation of Phase II/III development of INGREZZA in TD in Asia. In accordance with our continuing performance obligations, $10.2 million of the $30 million up-front payment is being deferred and recognized in future periods. Under the terms of the agreement, there is no general obligation to return the up-front payment for any non-contingent deliverable. No revenue was recognized under the Mitsubishi Tanabe agreement for the quarters ended March 31, 2018 or 2017. AbbVie Inc. (AbbVie). In June 2010, the Company announced an exclusive worldwide collaboration with AbbVie, to develop and commercialize elagolix and all next-generation GnRH antagonists (collectively, GnRH Compounds) for women’s and men’s health. AbbVie made an upfront payment of $75 million and has agreed to make additional development and regulatory event-based payments of up to $480 million, of which $75 million has been earned to date, and up to an additional $50 million in commercial event-based payments. Under the terms of the agreement, AbbVie is responsible for all third-party development, marketing and commercialization costs. The Company will be entitled to a percentage of worldwide sales of GnRH Compounds for the longer of ten years or the life of the related patent rights. AbbVie may terminate the collaboration at its discretion upon 180 days’ written notice to the Company. In such event, the Company would be entitled to specified payments for ongoing clinical development and related activities and all GnRH Compound product rights would revert to the Company. The Company has evaluated the terms of this agreement under Topic 606 and has determined that there is one performance obligation, the exclusive worldwide license with rights to develop, manufacture and commercialize elagolix. At execution, the transaction price included only the $75 million up-front consideration received. None of the development or regulatory milestones has been included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to AbbVie and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. During 2017, event-based revenue of $30.0 million was recognized based on AbbVie’s NDA submission for elagolix in endometriosis being accepted as filed by the FDA. During 2016, event-based revenue of $15.0 million was recognized related to AbbVie’s initiation of Phase III development of elagolix in uterine fibroids. No revenue was recognized under the AbbVie agreement for the quarters ended March 31, 2018 or 2017.

INVESTMENTS

3 Months Ended

Mar. 31, 2018

Investments Schedule [Abstract]

INVESTMENTS

3. INVESTMENTS

Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in comprehensive loss. The amortized cost of debt securities in this category is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion is included in investment income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in investment income or expense. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in investment income.

Investments consist of the following (in thousands):

	March 31, 2018		December 31, 2017
Commercial paper	$	41,993	$	75,362
Corporate debt securities		501,103		414,815
Securities of government sponsored entities		18,391		18,401
Total investments	$	561,487	$	508,578

The following is a summary of investments classified as available-for-sale securities (in thousands):

	Contractual Maturity (in years)	Amortized Cost		Gross Unrealized Gains⁽¹⁾		Gross Unrealized Losses⁽¹⁾			Aggregate Estimated Fair Value
March 31, 2018:
Classified as current assets:
Commercial paper	Less than 1	$	42,105	$	—	$	(112	)	$	41,993
Corporate debt securities	Less than 1		236,818		—		(1,127	)		235,691
Securities of government-sponsored entities	Less than 1		7,501		—		(17	)		7,484
Total short-term available-for-sale securities		$	286,424	$	—	$	(1,256	)	$	285,168
Classified as non-current assets:
Corporate debt securities	1 to 2	$	267,756	$	—	$	(2,344	)	$	265,412
Securities of government-sponsored entities	1 to 2		11,004		—		(97	)		10,907
Total long-term available-for-sale securities		$	278,760	$	—	$	(2,441	)	$	276,319
December 31, 2017:
Classified as current assets:
Commercial paper	Less than 1	$	75,396	$	1	$	(35	)	$	75,362
Corporate debt securities	Less than 1		178,776		—		(400	)		178,376
Securities of government-sponsored entities	Less than 1		7,503		—		(24	)		7,479
Total short-term available-for-sale securities		$	261,675	$	1	$	(459	)	$	261,217
Classified as non-current assets:
Corporate debt securities	1 to 2	$	237,749	$	—	$	(1,310	)	$	236,439
Securities of government-sponsored entities	1 to 2		11,004		—		(82	)		10,922
Total long-term available-for-sale securities		$	248,753	$	—	$	(1,392	)	$	247,361

(1)	Unrealized gains and losses are included in other comprehensive loss.

The following table presents gross unrealized losses and fair value for those available-for-sale investments that were in an unrealized loss position as of March 31, 2018 and December 31, 2017, aggregated by investment category and length of time that individual securities have been in a continuous loss position (in thousands):

	Less Than 12 Months					12 Months or Greater					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
March 31, 2018:
Commercial paper	$	41,993	$	(112	)	$	—	$	—		$	41,993	$	(112	)
Corporate debt securities		481,836		(3,409	)		19,267		(62	)		501,103		(3,471	)
Securities of government-sponsored entities		10,907		(97	)		7,484		(17	)		18,391		(114	)
Total	$	534,736	$	(3,618	)	$	26,751	$	(79	)	$	561,487	$	(3,697	)
December 31, 2017:
Commercial paper	$	62,602	$	(35	)	$	—	$	—		$	62,602	$	(35	)
Corporate debt securities		386,728		(1,660	)		28,087		(50	)		414,815		(1,710	)
Securities of government-sponsored entities		10,922		(82	)		7,479		(24	)		18,401		(106	)
Total	$	460,252	$	(1,777	)	$	35,566	$	(74	)	$	495,818	$	(1,851	)

The primary objective of the Company’s investment portfolio is to enhance overall returns in an efficient manner while maintaining safety of principal, prudent levels of liquidity and acceptable levels of risk. The Company’s investment policy limits interest-bearing security investments to certain types of instruments issued by institutions with primarily investment grade credit ratings and places restrictions on maturities and concentration by asset class and issuer.

The Company reviews the available-for-sale investments for other-than-temporary declines in fair value below cost basis each quarter and whenever events or changes in circumstances indicate that the cost basis of an asset may not be recoverable. This evaluation is based on a number of factors, including the length of time and the extent to which the fair value has been below the cost basis and adverse conditions related specifically to the security, including any changes to the credit rating of the security, and the intent to sell, or whether the Company will more likely than not be required to sell the security before recovery of its amortized cost basis. The assessment of whether a security is other-than-temporarily impaired could change in the future due to new developments or changes in assumptions related to any particular security. As of March 31, 2018 and December 31, 2017, the Company believed the cost bases for available-for-sale investments were recoverable in all material respects.

FAIR VALUE MEASUREMENTS

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

4. FAIR VALUE MEASUREMENTS

Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows:

Level 1:

Observable inputs such as quoted prices in active markets;

Level 2:

Inputs include quoted prices for similar instruments in active markets and/or quoted prices for identical or similar instruments in markets that are not active near the measurement date; and

Level 3:

Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

The Company classifies its cash equivalents and available for sale investments within Level 1 or Level 2. The fair value of the Company’s high quality investment grade corporate debt securities is determined using proprietary valuation models and analytical tools. These valuation models and analytical tools use market pricing or prices for similar instruments that are both objective and publicly available, including matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids and/or offers. The Company did not reclassify any investments between levels in the fair value hierarchy during the three months ended March 31, 2018.

The Company’s assets which were measured at fair value on a recurring basis as of March 31, 2018 and December 31, 2017 were determined using the inputs described above and are as follows (in millions):

				Fair Value Measurements Using
	Carrying Value			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
March 31, 2018:
Classified as current assets:
Cash and money market funds	$	147.4		$	147.4		$	—		$	—
Commercial paper		69.9			—			69.9			—
Securities of government-sponsored entities		7.5			—			7.5			—
Corporate debt securities		235.7			—			235.7			—
Subtotal		460.5			147.4			313.1			—
Classified as long-term assets:
Cash and money market funds		1.5			1.5			—			—
Certificates of deposit		3.0			3.0			—			—
Securities of government-sponsored entities		10.9			—			10.9			—
Corporate debt securities		265.4			—			265.4			—
Total		741.3			151.9			589.4			—
Less cash, cash equivalents and restricted cash		(179.8	)		(151.9	)		(27.9	)		—
Total investments	$	561.5		$	-		$	561.5		$	—
December 31, 2017:
Classified as current assets:
Cash and money market funds	$	170.2		$	170.2		$	—		$	—
Commercial paper		159.9			—			159.9			—
Securities of government-sponsored entities		7.5			—			7.5			—
Corporate debt securities		178.4			—			178.4			—
Subtotal		516.0			170.2			345.8			—
Classified as long-term assets:
Cash and money market funds		1.5			1.5			—			—
Certificates of deposit		3.0			3.0			—			—
Securities of government-sponsored entities		10.9			—			10.9			—
Corporate debt securities		236.4			—			236.4			—
Total		767.8			174.7			593.1			—
Less cash, cash equivalents and restricted cash		(259.2	)		(174.6	)		(84.6	)		—
Total investments	$	508.6		$	0.1		$	508.5		$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

CONVERTIBLE SENIOR NOTES

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

CONVERTIBLE SENIOR NOTES

5. CONVERTIBLE SENIOR NOTES

On May 2, 2017, the Company completed a private placement of $517.5 million in aggregate principal amount of 2.25% convertible senior notes due 2024 (2024 Notes) and entered into an indenture agreement (2024 Indenture) with respect to the 2024 Notes. The 2024 Notes accrue interest at a fixed rate of 2.25% per year, payable semiannually in arrears on May 15 and November 15 of each year, beginning on November 15, 2017. The 2024 Notes mature on May 15, 2024. The net proceeds from the issuance of the 2024 Notes were approximately $502.8 million, after deducting commissions and the offering expenses payable by the Company.

Holders of the 2024 Notes may convert the 2024 Notes at any time prior to the close of business on the business day immediately preceding May 15, 2024, only under the following circumstances:

(i)

during any calendar quarter commencing after the calendar quarter ending on September 30, 2017 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than 130% of the conversion price on each applicable trading day;

(ii)

during the five business-day period immediately after any five consecutive trading-day period (the ‘‘measurement period’’) in which the trading price (as defined in the 2024 Indenture) per $1,000 principal amount of the 2024 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day;

(iii)

upon the occurrence of specified corporate events, including a merger or a sale of all or substantially all of the Company’s assets; or

(iv)

if the Company calls the 2024 Notes for redemption, until the close of business on the business day immediately preceding the redemption date.

On or after January 15, 2024, until the close of business on the scheduled trading day immediately preceding May 15, 2024, holders may convert their 2024 Notes at any time.

Upon conversion, holders will receive the principal amount of their 2024 Notes and any excess conversion value, calculated based on the per share volume-weighted average price for each of the 30 consecutive trading days during the observation period (as more fully described in the 2024 Indenture). For both the principal and excess conversion value, holders may receive cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s option.

It is the Company’s intent and policy to settle conversions through combination settlement, which essentially involves repayment of an amount of cash equal to the “principal portion” and delivery of the “share amount” in excess of the principal portion in shares of common stock or cash. In general, for each $1,000 in principal, the “principal portion” of cash upon settlement is defined as the lesser of $1,000, and the conversion value during the 25-day observation period as described in the indenture for the notes. The conversion value is the sum of the daily conversion value which is the product of the effective conversion rate divided by 25 days and the daily volume weighted average price (VWAP) of the Company’s common stock. The “share amount” is the cumulative “daily share amount” during the observation period, which is calculated by dividing the daily VWAP into the difference between the daily conversion value (i.e., conversion rate x daily VWAP) and $1,000.

The initial conversion rate for the 2024 Notes is 13.1711 shares of common stock per $1,000 principal amount, which is equivalent to an initial conversion price of approximately $75.92 per share of the Company’s common stock. The conversion rate will be subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. The initial conversion price of the 2024 Notes represents a premium of approximately 42.5% to the closing sale price of $53.28 per share of the Company’s common stock on the NASDAQ Global Select Market on April 26, 2017, the date that the Company priced the private offering of the 2024 Notes.

In the event of conversion, holders would forgo all future interest payments, any unpaid accrued interest and the possibility of further stock price appreciation. Upon the receipt of conversion requests, the settlement of the 2024 Notes will be paid pursuant to the terms of the 2024 Indenture. In the event that all of the 2024 Notes are converted, the Company would be required to repay the $517.5 million in principal value and any conversion premium in any combination of cash and shares of its common stock (at the Company’s option).

Prior to May 15, 2021, the Company may not redeem the 2024 Notes. On or after May 15, 2021, the Company may redeem for cash all or part of the 2024 Notes if the last reported sale price (as defined in the 2024 Indenture) of the Company’s common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading-day period ending on, and including, the trading day immediately before the date which the Company provides notice of redemption. The redemption price will equal the sum of (i) 100% of the principal amount of the 2024 Notes being redeemed, plus (ii) accrued and unpaid interest, including additional interest, if any, to, but excluding, the redemption date. No sinking fund is provided for the 2024 Notes.

If the Company undergoes a fundamental change, as defined in the 2024 Indenture, subject to certain conditions, holders of the 2024 Notes may require the Company to repurchase for cash all or part of their 2024 Notes at a repurchase price equal to 100% of the principal amount of the 2024 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, if a ‘‘make-whole fundamental change’’ (as defined in the 2024 Indenture) occurs prior to January 15, 2024, the Company will, in certain circumstances, increase the conversion rate for a holder who elects to convert its notes in connection with the make-whole fundamental change.

The 2024 Notes are the Company’s general unsecured obligations that rank senior in right of payment to all of its indebtedness that is expressly subordinated in right of payment to the 2024 Notes, and equal in right of payment to the Company’s unsecured indebtedness.

The fair value of the 2024 Notes is estimated utilizing market quotations from an over-the-counter trading market. As of March 31, 2018, the fair value approximated 131.25 percent of the face principal amount of the 2024 Notes.

While the 2024 Notes are currently classified on the Company’s consolidated balance sheet at March 31, 2018 and December 31, 2017 as long-term, the future convertibility and resulting balance sheet classification of this liability will be monitored at each quarterly reporting date and will be analyzed dependent upon market prices of the Company’s common stock during the prescribed measurement periods. In the event that the holders of the 2024 Notes have the election to convert the 2024 Notes at any time during the prescribed measurement period, the 2024 Notes would then be considered a current obligation and classified as such.

Under current accounting guidance, an entity must separately account for the liability and equity components of convertible debt instruments (such as the 2024 Notes) that may be settled entirely or partially in cash upon conversion in a manner that reflects the issuer’s economic interest cost. The liability component of the instrument was valued in a manner that reflects the market interest rate for a similar nonconvertible instrument at the date of issuance. The initial carrying value of the liability component of $368.3 million was calculated using a 7.5% assumed borrowing rate. The equity component of $149.2 million, representing the conversion option, was determined by deducting the fair value of the liability component from the par value of the 2024 Notes and is recorded in additional paid-in capital on the consolidated balance sheet at the issuance date. That equity component is treated as a discount on the liability component of the 2024 Notes, which is amortized over the seven year term of the 2024 Notes using the effective interest rate method. The equity component is not re-measured as long as it continues to meet the conditions for equity classification.

The Company allocated the total transaction costs of approximately $14.7 million related to the issuance of the 2024 Notes to the liability and equity components of the 2024 Notes based on their relative values. Transaction costs attributable to the liability component are amortized to interest expense over the seven-year term of the 2024 Notes, and transaction costs attributable to the equity component are netted with the equity component in stockholders’ equity.

The 2024 Notes do not contain any financial or operating covenants or any restrictions on the payment of dividends, the issuance of other indebtedness or the issuance or repurchase of securities by the Company. The 2024 Indenture contains customary events of default with respect to the 2024 Notes, including that upon certain events of default, 100% of the principal and accrued and unpaid interest on the 2024 Notes will automatically become due and payable.

Debt, net of discounts and deferred financing costs at March 31, 2018 and December 31, 2017, consisted of the following (in thousands):

	March 31, 2018			December 31, 2017
Principal	$	517,500		$	517,500
Deferred financing costs		(9,326	)		(9,652	)
Debt discount, net		(133,965	)		(138,230	)
Net carrying amount	$	374,209		$	369,618

SHARE-BASED COMPENSATION

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

SHARE-BASED COMPENSATION

6. SHARE-BASED COMPENSATION

The compensation expense related to the Company’s share-based compensation arrangements has been included in the condensed consolidated statements of comprehensive loss as follows (in thousands):

	Three Months Ended March 31,
	2018		2017
General and administrative	$	7,256	$	5,453
Research and development		12,623		3,523
Total share-based compensation expense	$	19,879	$	8,976

The fair value of equity instruments that vest based on continued employee service is recognized and amortized on a straight-line basis over the requisite service period. For restricted stock units (RSUs) with performance-based vesting requirements (PRSUs), no expense is recorded until the performance condition is probable of being achieved. During the three months ended March 31, 2018, the Company recorded a non-recurring share-based compensation charge of $7.7 million related to the modification of certain options and RSUs.

As of March 31, 2018, total unrecognized estimated compensation cost related to non-vested stock options and non-vested RSUs, that vest over a given service period, granted prior to that date was $67.7 million and $62.0 million, respectively, which is expected to be recognized over a weighted average period of approximately 3.2 and 3.3 years, respectively. Additionally, the Company has approximately 0.4 million PRSUs outstanding. As of March 31, 2018, total unrecognized estimated compensation cost related to these PRSUs was $21.5 million and will be recognized over the expected performance period once the achievement of performance conditions becomes probable.

During the three months ended March 31, 2018 and 2017, stock options to purchase approximately 0.7 million and 0.3 million shares of the Company’s common stock were exercised, respectively. The cash received by the Company from stock option exercises during the three months ended March 31, 2018 and 2017 was approximately $16.1 million and $1.5 million, respectively. The Company also issued approximately 0.4 million and 0.3 million shares of common stock pursuant to the vesting of RSUs during each of the three months ended March 31, 2018 and 2017.

Stock Option Assumptions

The Company granted stock options to purchase approximately 0.8 million and 1.4 million shares of the Company’s common stock during the three months ended March 31, 2018 and 2017, respectively. These stock options generally vest monthly over a four-year period. The exercise price of all stock options granted during the three months ended March 31, 2018 and 2017 was equal to the closing price of the Company’s common stock on the date of grant. The estimated fair value of each stock option granted was determined on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions for the stock option grants:

	Three Months Ended March 31,
	2018	2017
Risk-free interest rate	2.4%	2.0%
Expected volatility of common stock	60.6%	58.1%
Dividend yield	0.0%	0.0%
Expected option term	4.7 years	5.8 years

The Black-Scholes option-pricing model incorporates various and highly sensitive assumptions including expected volatility, expected term and interest rates. The expected volatility is based on the historical volatility of the Company’s common stock over the most recent period commensurate with the estimated expected term of the Company’s stock options. The expected option term is estimated based on historical experience as well as the status of the employee. For example, directors and officers have a longer expected option term than all other employees. The risk-free rate for periods within the contractual life of the option is based upon observed interest rates appropriate for the expected term of the Company’s employee stock options. The Company has never declared or paid dividends and has no plans to do so in the foreseeable future. For the three months ended March 31, 2018 and 2017, share-based compensation expense related to stock options was $13.6 million and $5.7 million, respectively.

Restricted Stock Units

During the three months ended March 31, 2018 and 2017, the Company granted approximately 0.5 million and 0.4 million RSUs, respectively, that vest annually over a four-year period. Additionally, during the three months ended March 31, 2018, the Company granted approximately 0.2 million PRSUs. No PRSUs were granted during 2017. The Company’s PRSUs vest based on the achievement of pre-defined Company-specific performance criteria and expire approximately four to five years from the grant date. Expense recognition for PRSUs commences when attainment of the performance based criteria is probable. The fair value of RSUs and PRSUs is estimated based on the closing sale price of the Company’s common stock on the date of grant. For the three months ended March 31, 2018 and 2017, the aggregate share-based compensation expense related to RSUs and PRSUs was $6.3 million and $3.3 million, respectively.

ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Description of Business	Description of Business. Neurocrine Biosciences, Inc. (the Company or Neurocrine) was incorporated in California in 1992 and reincorporated in Delaware in 1996. The Company discovers, develops and commercializes innovative and life-changing pharmaceuticals, in diseases with high unmet medical needs, through its novel research and development (R&D) platform, focused on neurological and endocrine based diseases and disorders. In April 2017, the Company received approval from the United States Food and Drug Administration (FDA) for INGREZZA^® (valbenazine), a vesicular monoamine transporter 2 (VMAT2) inhibitor for the treatment of tardive dyskinesia. The Company’s three lead late-stage clinical programs are elagolix, a gonadotropin-releasing hormone (GnRH) antagonist for women’s health that is partnered with AbbVie Inc. (AbbVie), INGREZZA for Tourette syndrome, and opicapone, a highly-selective catechol-O-methyltransferase inhibitor for the treatment of Parkinson’s disease.
Basis of Presentation	Basis of Presentation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (GAAP) for interim financial information and with the instructions of the Securities and Exchange Commission (SEC) on Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for complete financial statements. In the opinion of management, the condensed consolidated financial statements include all adjustments necessary, which are of a normal and recurring nature, for the fair presentation of the Company’s financial position and of the results of operations and cash flows for the periods presented. The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. These financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2017 included in the Company’s Annual Report on Form 10-K filed with the SEC. The results of operations for the interim period shown in this report are not necessarily indicative of the results that may be expected for any other interim period or for the full year. The balance sheet at December 31, 2017 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements.
Impact of Recently Issued Accounting Standards	Impact of Recently Issued Accounting Standards. In May 2014 the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. This new standard amends the guidance for the recognition of revenue from contracts with customers to transfer goods and services. The FASB subsequently issued additional, clarifying standards to address issues arising from implementation of the new revenue recognition standard. The Company adopted this new standard as of January 1, 2018 using the modified retrospective method. The adoption of the new revenue standards did not change the Company’s revenue recognition. As the Company did not identify any accounting changes that impacted the amount of reported revenues with respect to product revenues, or revenue from collaboration and license agreements, no adjustment to retained earnings was required upon adoption. See below for discussion of the Company’s Revenue Recognition policy. In February 2016, the FASB issued ASU 2016-02 Leases. This update amends the current accounting guidance for lease transactions. Under the new guidance, a lessee will be required to recognize both assets and liabilities for any leases in excess of twelve months. Additionally, certain qualitative and quantitative disclosures will also be required in the financial statements. The Company is required to adopt this new guidance beginning in 2019 and early adoption is permitted. The Company’s lease for its corporate headquarters is subject to this new guidance and the Company is in the process of determining the impact of the adoption of this update will have on its condensed consolidated financial statements is ongoing. In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash”, which clarifies the presentation of restricted cash and restricted cash equivalents in the statements of cash flows. Under this ASU, restricted cash and restricted cash equivalents are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts presented on the statements of cash flows. This ASU is intended to reduce diversity in practice in the classification and presentation of changes in restricted cash on the statement of cash flows. This ASU requires that the statement of cash flows explain the change in total cash and equivalents and amounts generally described as restricted cash or restricted cash equivalents when reconciling the beginning-of-period and end-of-period total amounts. This ASU also requires a reconciliation between the total of cash and equivalents and restricted cash presented on the statement of cash flows and the cash and equivalents balance presented on the balance sheet. This amended guidance was retrospectively adopted on January 1, 2018 and required that cash, cash equivalents and restricted cash reported on the Condensed Consolidated Statements of Cash Flows now includes restricted cash of $4.5 million and $5.1 million as of March 31, 2018 and 2017, respectively, as well as previously reported cash and cash equivalents.
Use of Estimates	Use of Estimates. The preparation of the condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and the accompanying notes. Actual results could differ from those estimates.
Inventory	Inventory. Inventory is stated at the lower of cost or estimated net realizable value. The Company currently uses actual costing to determine the cost basis for its inventory. Inventory is valued on a first-in, first-out basis and consists primarily of third-party manufacturing costs. The Company capitalizes inventory costs associated with its products upon regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed. Prior to FDA approval of INGREZZA, all costs related to its manufacturing were charged to research and development expense in the period incurred. At March 31, 2018 and December 31, 2017, the Company’s physical inventory included active pharmaceutical product (API) that had been produced prior to FDA approval of INGREZZA and accordingly has no cost basis as the cost associated with producing this material was expensed rather than capitalized in accordance with authoritative guidance. Additionally, manufacturing of bulk drug product, finished bottling and other labeling activities that occurred post FDA approval are included in the inventory value at March 31, 2018 and December 31, 2017. The Company provides reserves for potential excess, dated or obsolete inventory based on an analysis of forecasted demand compared to quantities on hand and any firm purchase orders, as well as product shelf life. To date, the Company has determined that such reserves are not required.
Cost of Product Sales	Cost of Product Sales. Cost of product sales consists of third-party manufacturing costs, transportation and freight, and indirect overhead costs associated with the manufacture and distribution of INGREZZA. Cost of product sales may also include period costs related to certain inventory manufacturing services, inventory adjustment charges as well as manufacturing variances. A significant portion of the cost of producing the product sold to date was expensed as R&D prior to the Company’s New Drug Application (NDA) approval for INGREZZA and therefore is not included in the cost of product sales during this period.
Accounts Receivable	Accounts Receivable. Accounts receivable are recorded net of customer allowances for prompt payment discounts, chargebacks, and any allowance for doubtful accounts. The Company estimates the allowance for doubtful accounts based on existing contractual payment terms, actual payment patterns of its customers and individual customer circumstances. To date, the Company has determined that an allowance for doubtful accounts is not required.
Research and Development Expenses	Research and Development Expenses. R&D expenses consist primarily of salaries, payroll taxes, employee benefits, and share-based compensation charges, for those individuals involved in ongoing R&D efforts; as well as scientific contractor fees, development milestones from in-licensed collaboration agreements, preclinical and clinical trial costs, R&D facilities costs, laboratory supply costs, and depreciation of scientific equipment. All such costs are charged to R&D expense as incurred. These expenses result from the Company’s independent R&D efforts as well as efforts associated with collaborations and in-licensing arrangements. In addition, the Company funds R&D at other companies and research institutions under agreements, which are generally cancelable. The Company reviews and accrues clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of patient studies and other events. The Company follows this method since reasonably dependable estimates of the costs applicable to various stages of a research agreement or clinical trial can be made. Accrued clinical costs are subject to revisions as trials progress. Revisions are charged to expense in the period in which the facts that give rise to the revision become known.
Revenue Recognition	Revenue Recognition. Effective January 1, 2018, the Company adopted Topic 606, using the modified retrospective method, which it elected to apply to all contracts. As the Company did not identify any revenue recognition differences when comparing the revenue recognition criteria under Topic 606 to the requirements under previous criteria with respect to product revenues, or revenue from collaboration and license agreements, no cumulative effect adjustment to retained earnings was necessary upon adoption. See the Company’s Annual Report on Form 10-K filed with the SEC for the year ended December 31, 2017 for a detailed description of the Company’s accounting policy under Topic 605 which was effective for periods prior to January 1, 2018. The Company’s revenues for the first quarter of 2018, had the Company continued to account for revenue recognition under Topic 605, would not have differed by a significant amount from those reported under Topic 606. Under Topic 606, the Company recognizes revenues when its customers obtain control of its products or services in an amount that reflects the consideration it expects to receive from its customers in exchange for those products or services. To determine revenue recognition, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies the performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. If the consideration promised under the contract includes a variable amount, the Company must estimate the consideration it expects to receive for transferring the good or service to the customer. There are two methods for determining the amount of variable consideration: (i) the expected value method, which is the sum of probability-weighted amounts in a range of possible consideration amounts, and; (ii) the mostly likely amount method, which identifies the single most likely amount in a range of possible consideration amounts. Performance milestone payments represent a form of variable consideration.
Product Sales, Net	Product Sales, Net. The Company’s product sales consist of U.S. sales of INGREZZA. INGREZZA was approved by the FDA on April 11, 2017 and the Company commenced shipments of INGREZZA to select pharmacies (SPs) and a select distributor (SD), or collectively, its customers, in late April 2017. The SPs dispense product to a patient based on the fulfillment of a prescription and the SD sells product to government facilities, long-term care pharmacies or in-patient hospital pharmacies. The Company’s agreements with the SPs and SD provide for transfer of title to the product at the time the product is delivered to the SP or SD. In addition, except for limited circumstances, the SPs and SDs have no right of product return to the Company. Product sales are recognized when the customer obtains control of the Company’s product, typically upon delivery to the customer. Revenue from product sales are recorded at the net sales price (transaction price), which includes an estimate of variable consideration for which reserves are established and which results from contractual discounts, returns, chargebacks, rebates, co-pay assistance and other allowances relating to the Company’s sales of its products. These reserves are based on the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if the amount is payable to the customer) or a current liability (if the amount is payable to a party other than a customer). Where appropriate, these estimates take into consideration a range of possible outcomes that are probability-weighted for relevant factors such as the Company’s historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained, and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. The following are the Company’s significant categories of sales discounts and allowances: Trade Discounts and Allowances: The Company generally provides customers with discounts that include prompt payment discounts, discounts for providing sales data, and other off-invoice discounts that are explicitly stated in the Company’s contracts and are recorded as a reduction of revenue in the period the related product revenue is recognized. Product Returns: The Company offers customers limited product return rights for damages and shipment errors provided it is within a very limited period after the original shipping date as set forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient or for drug expiration. The Company receives real-time shipping reports and inventory reports from the customers and has the ability to control the amount of product that is sold to the customers. Product returns to date have not been significant and the Company has not considered it necessary to record a reserve for product returns. Government Rebates: The Company is subject to discount obligations under state Medicaid programs and Medicare prescription drug coverage gap program. The Company estimates its Medicaid and Medicare prescription drug coverage gap rebates based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability that is included in accrued expenses on the condensed consolidated balance sheet. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. Provider Chargebacks and Discounts: Chargebacks for fees and discounts to providers represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to customers who directly purchase the product from the Company. Customers charge the Company for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. These reserves are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider by customers, and the Company generally issues credits for such amounts following the customer’s notification to the Company of the resale. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at each reporting period end that the Company expects will be sold to qualified healthcare providers. Co-Payment Assistance: The Company offers co-payment assistance to commercially insured patients meeting certain eligibility requirements. The calculation of the accrual for co-pay assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. Shipping and handling costs related to the Company’s product sales are included in selling, general and administrative expenses.
Collaborative Research and Development Agreements	Collaborative Research and Development Agreements The Company enters into collaboration and licensing agreements that are within the scope of Topic 606, under which it licenses certain rights to its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services; and royalties on net sales of licensed products. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success. Licenses of Intellectual Property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, commercialization and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect milestone and license fees revenues and earnings in the period of adjustment. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its out-licensing arrangements. The Company receives payments from its licensees based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.

INVESTMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Investments Schedule [Abstract]

Investments

Investments consist of the following (in thousands):

	March 31, 2018		December 31, 2017
Commercial paper	$	41,993	$	75,362
Corporate debt securities		501,103		414,815
Securities of government sponsored entities		18,391		18,401
Total investments	$	561,487	$	508,578

Summary of Investments Classified as Available-For-Sale Securities

The following is a summary of investments classified as available-for-sale securities (in thousands):

	Contractual Maturity (in years)	Amortized Cost		Gross Unrealized Gains⁽¹⁾		Gross Unrealized Losses⁽¹⁾			Aggregate Estimated Fair Value
March 31, 2018:
Classified as current assets:
Commercial paper	Less than 1	$	42,105	$	—	$	(112	)	$	41,993
Corporate debt securities	Less than 1		236,818		—		(1,127	)		235,691
Securities of government-sponsored entities	Less than 1		7,501		—		(17	)		7,484
Total short-term available-for-sale securities		$	286,424	$	—	$	(1,256	)	$	285,168
Classified as non-current assets:
Corporate debt securities	1 to 2	$	267,756	$	—	$	(2,344	)	$	265,412
Securities of government-sponsored entities	1 to 2		11,004		—		(97	)		10,907
Total long-term available-for-sale securities		$	278,760	$	—	$	(2,441	)	$	276,319
December 31, 2017:
Classified as current assets:
Commercial paper	Less than 1	$	75,396	$	1	$	(35	)	$	75,362
Corporate debt securities	Less than 1		178,776		—		(400	)		178,376
Securities of government-sponsored entities	Less than 1		7,503		—		(24	)		7,479
Total short-term available-for-sale securities		$	261,675	$	1	$	(459	)	$	261,217
Classified as non-current assets:
Corporate debt securities	1 to 2	$	237,749	$	—	$	(1,310	)	$	236,439
Securities of government-sponsored entities	1 to 2		11,004		—		(82	)		10,922
Total long-term available-for-sale securities		$	248,753	$	—	$	(1,392	)	$	247,361

(1)	Unrealized gains and losses are included in other comprehensive loss.

Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position

	Less Than 12 Months					12 Months or Greater					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
March 31, 2018:
Commercial paper	$	41,993	$	(112	)	$	—	$	—		$	41,993	$	(112	)
Corporate debt securities		481,836		(3,409	)		19,267		(62	)		501,103		(3,471	)
Securities of government-sponsored entities		10,907		(97	)		7,484		(17	)		18,391		(114	)
Total	$	534,736	$	(3,618	)	$	26,751	$	(79	)	$	561,487	$	(3,697	)
December 31, 2017:
Commercial paper	$	62,602	$	(35	)	$	—	$	—		$	62,602	$	(35	)
Corporate debt securities		386,728		(1,660	)		28,087		(50	)		414,815		(1,710	)
Securities of government-sponsored entities		10,922		(82	)		7,479		(24	)		18,401		(106	)
Total	$	460,252	$	(1,777	)	$	35,566	$	(74	)	$	495,818	$	(1,851	)

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Assets Measured at Fair Value on Recurring Basis

				Fair Value Measurements Using
	Carrying Value			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
March 31, 2018:
Classified as current assets:
Cash and money market funds	$	147.4		$	147.4		$	—		$	—
Commercial paper		69.9			—			69.9			—
Securities of government-sponsored entities		7.5			—			7.5			—
Corporate debt securities		235.7			—			235.7			—
Subtotal		460.5			147.4			313.1			—
Classified as long-term assets:
Cash and money market funds		1.5			1.5			—			—
Certificates of deposit		3.0			3.0			—			—
Securities of government-sponsored entities		10.9			—			10.9			—
Corporate debt securities		265.4			—			265.4			—
Total		741.3			151.9			589.4			—
Less cash, cash equivalents and restricted cash		(179.8	)		(151.9	)		(27.9	)		—
Total investments	$	561.5		$	-		$	561.5		$	—
December 31, 2017:
Classified as current assets:
Cash and money market funds	$	170.2		$	170.2		$	—		$	—
Commercial paper		159.9			—			159.9			—
Securities of government-sponsored entities		7.5			—			7.5			—
Corporate debt securities		178.4			—			178.4			—
Subtotal		516.0			170.2			345.8			—
Classified as long-term assets:
Cash and money market funds		1.5			1.5			—			—
Certificates of deposit		3.0			3.0			—			—
Securities of government-sponsored entities		10.9			—			10.9			—
Corporate debt securities		236.4			—			236.4			—
Total		767.8			174.7			593.1			—
Less cash, cash equivalents and restricted cash		(259.2	)		(174.6	)		(84.6	)		—
Total investments	$	508.6		$	0.1		$	508.5		$	—

Significant Collaborative Research and Development Agreements - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Jun. 30, 2010	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mitsubishi Tanabe
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front license fees						$ 30,000,000
Collaborative agreement maximum additional payment to receive						85,000,000
Patent rights period		The longer of ten years or the life of the related patent rights.
Collaborative arrangement right description		Under the terms of the Company’s agreement with Mitsubishi Tanabe, the collaboration effort between the parties to advance INGREZZA towards commercialization in Japan and other select Asian markets is governed by a joint steering committee and joint development committee with representatives from both the Company and Mitsubishi Tanabe. There are no performance, cancellation, termination or refund provisions in the agreement that would have a material financial consequence to the Company. The Company does not directly control when event-based payments will be achieved or when royalty payments will begin. Mitsubishi Tanabe may terminate the agreement at its discretion upon 180 days’ written notice to the Company. In such event, all INGREZZA product rights for Japan and other select Asian markets would revert to the Company.
Collaboration termination notice period		180 days
Revenues recognized under collaboration agreement		$ 0	$ 0	$ 15,000,000		19,800,000
Deferred revenues under collaboration						$ 10,200,000
Mitsubishi Tanabe \| Topic 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Clinical trial cost		12,000,000
Up-front consideration received		$ 30,000,000
AbbVie
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front license fees	$ 75,000,000
Patent rights period		Ten years or the life of the related patent rights.
Collaborative arrangement right description		The Company will be entitled to a percentage of worldwide sales of GnRH Compounds for the longer of ten years or the life of the related patent rights.
Collaboration termination notice period		180 days
Revenues recognized under collaboration agreement		$ 0	$ 0	$ 30,000,000	$ 15,000,000
AbbVie \| Development and Regulatory Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative agreement maximum additional payment to receive		480,000,000
Collaborative agreement payment received		75,000,000
AbbVie \| Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative agreement maximum additional payment to receive		50,000,000
AbbVie \| Topic 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front consideration received		$ 75,000,000

Summary of Investments Classified as Available-For-Sale Securities (Detail) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Mar. 31, 2018

Dec. 31, 2017

Schedule Of Available For Sale Securities [Line Items]

Aggregate Estimated Fair Value

$ 561,487

$ 508,578

Commercial paper

Schedule Of Available For Sale Securities [Line Items]

Aggregate Estimated Fair Value

41,993

75,362

Corporate debt securities

Schedule Of Available For Sale Securities [Line Items]

Aggregate Estimated Fair Value

501,103

414,815

Domestic and foreign government agencies debt securities

Schedule Of Available For Sale Securities [Line Items]

Aggregate Estimated Fair Value

18,391

18,401

Short-term investments

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

286,424

261,675

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(1,256)

(459)

Aggregate Estimated Fair Value

285,168

261,217

Short-term investments | Commercial paper

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

42,105

75,396

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(112)

(35)

Aggregate Estimated Fair Value

$ 41,993

$ 75,362

Short-term investments | Commercial paper | Maximum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Short-term investments | Corporate debt securities

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

$ 236,818

$ 178,776

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(1,127)

(400)

Aggregate Estimated Fair Value

$ 235,691

$ 178,376

Short-term investments | Corporate debt securities | Maximum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Short-term investments | Domestic and foreign government agencies debt securities

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

$ 7,501

$ 7,503

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(17)

(24)

Aggregate Estimated Fair Value

$ 7,484

$ 7,479

Short-term investments | Domestic and foreign government agencies debt securities | Maximum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Long-term investments

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

$ 278,760

$ 248,753

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(2,441)

(1,392)

Aggregate Estimated Fair Value

276,319

247,361

Long-term investments | Corporate debt securities

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

267,756

237,749

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(2,344)

(1,310)

Aggregate Estimated Fair Value

$ 265,412

$ 236,439

Long-term investments | Corporate debt securities | Minimum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Long-term investments | Corporate debt securities | Maximum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

2 years

Long-term investments | Domestic and foreign government agencies debt securities

Schedule Of Available For Sale Securities [Line Items]

Amortized Cost

$ 11,004

Gross Unrealized Gains

^[1]

Gross Unrealized Losses

^[1]

(97)

(82)

Aggregate Estimated Fair Value

$ 10,907

$ 10,922

Long-term investments | Domestic and foreign government agencies debt securities | Minimum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Long-term investments | Domestic and foreign government agencies debt securities | Maximum

Schedule Of Available For Sale Securities [Line Items]

Available for sale securities contractual maturity

2 years

[1]	Unrealized gains and losses are included in other comprehensive loss.

Convertible Senior Notes - Additional Information (Detail)		3 Months Ended
	May 02, 2017 USD ($)	Mar. 31, 2018 USD ($) d $ / shares	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Convertible senior notes principal amount		$ 517,500,000	$ 517,500,000
2.25% Convertible Senior Notes due 2024
Debt Instrument [Line Items]
Convertible senior notes principal amount	$ 517,500,000
Convertible senior notes interest percentage	2.25%
Convertible senior notes interest rate	2.25%
Convertible senior notes convertible latest date		May 15, 2024
Proceeds from Senior Convertible Notes	$ 502,800,000
Threshold common stock trading days \| d		20
Threshold consecutive common stock trading days \| d		30
Threshold percentage of common stock price trigger		130.00%
Debt instrument conversion obligation number of consecutive business days after consecutive trading day period		5 days
Debt instrument conversion obligation period of consecutive trading days.		5 days
Principal amount on conversion rate		$ 1,000
Minimum percentage of common stock price trigger		98.00%
Debt instrument convertible trading days during observation period		30 days
Conversion Observation Period		25 days
Debt instrument conversion value description		The conversion value is the sum of the daily conversion value which is the product of the effective conversion rate divided by 25 days and the daily volume weighted average price (VWAP) of the Company’s common stock.
Debt instrument conversion share amount description		The “share amount” is the cumulative “daily share amount” during the observation period, which is calculated by dividing the daily VWAP into the difference between the daily conversion value (i.e., conversion rate x daily VWAP) and $1,000.
Convertible senior notes convertible in to shares		0.00131711
Convertible senior notes conversion price \| $ / shares		$ 75.92
Market Price of Common stock \| $ / shares		$ 53.28
Convertible senior note premium		42.50%
Convertible senior notes redemption rate		100.00%
Fair value of convertible senior note as percentage of principal amount		131.25%
Convertible senior note carrying value of the liability component		$ 368,300,000
Convertible senior note assumed borrowing rate		7.50%
Convertible senior note carrying value of the equity component		$ 149,200,000
Convertible senior notes		7 years
Transaction cost related to issuance of convertible senior note		$ 14,700,000
Debt instrument events of default percentage of principal and accrued and unpaid interest due and payable upon default		100.00%

Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-recurring share-based compensation charge, recorded	$ 7,700
Stock option exercised	700,000	300,000
Cash received from stock option exercises	$ 16,100	$ 1,500
Common stock issued pursuant to the vesting of restricted stock units (RSUs)	400,000	300,000
Stock options granted	800,000	1,400,000
Share-based compensation expense	$ 19,879	$ 8,976
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost	$ 67,700
Stock vesting period	3 years 2 months 12 days
Stock vesting period	4 years	4 years
Share-based compensation expense	$ 13,600	$ 5,700
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost	$ 62,000
Stock vesting period	3 years 3 months 18 days
Stock vesting period	4 years	4 years
Share-based compensation expense	$ 6,300	$ 3,300
Restricted stock units granted	500,000	400,000
Performance-based RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost	$ 21,500
RSU with performance-based vesting requirements outstanding	400,000
Restricted stock units granted	200,000	0
Performance-based RSUs \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock vesting period	4 years
Performance-based RSUs \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock vesting period	5 years

Real Estate - Additional Information (Detail) $ in Millions	1 Months Ended	3 Months Ended			12 Months Ended
Real Estate - Additional Information (Detail) $ in Millions	Dec. 31, 2007 USD ($) Building	Mar. 31, 2018 USD ($) ft² RenewalOption Lease_Agreements	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2008 USD ($)
Real Estate Properties [Line Items]
Sale of facility and associated real property	$ 109.0
Mortgage debt retired	47.7
Cash received net of transaction costs and debt retirement	$ 61.0
Leaseback transaction lease period	12 years
Number of building leased \| Building	2
Net deferred gain on real estate sale		$ 8.6				$ 39.1
Deferred gain recognized on real estate sale		$ 0.2		$ 0.9
Lease expiration year		2029
Percentage of management fee included in the base annual rent					3.50%
Lease security deposit					$ 4.7
Letter of credit					$ 3.0
Number of times to renew the lease contract \| RenewalOption		2
Lease extension period		10 years
Subleased agreement area \| ft²		16,000
Rental income from sublease agreement		$ 0.3
Sublease
Real Estate Properties [Line Items]
Number of sublease agreements \| Lease_Agreements		1
Reversal of cease use expense			$ 0.5
Second Sublease
Real Estate Properties [Line Items]
Lease expiration date		2018-03
Amended Lease Term
Real Estate Properties [Line Items]
Lease expiration date		Dec. 31, 2029
Percentage reduction in base rental					8.00%
Tenant improvement allowances					$ 13.1
Lease security deposit					$ 3.0

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	220,000,000	220,000,000
Common stock, shares issued	89,882,062	88,793,903
Common stock, shares outstanding	89,882,062	88,793,903

STOCKHOLDERS' EQUITY	3 Months Ended
STOCKHOLDERS' EQUITY	Mar. 31, 2018
Equity [Abstract]
STOCKHOLDERS' EQUITY	7. STOCKHOLDERS’ EQUITY Shelf Registration Statements In February 2017, the Company filed an automatic shelf registration statement which immediately became effective by rule of the SEC. For so long as the Company continues to satisfy the requirements to be deemed a well-known seasoned issuer, this shelf registration statement allows the Company to issue an unlimited number of securities from time to time. As of March 31, 2018, the Company had not sold any securities under this shelf registration statement. The specific terms of future offerings, if any, under this shelf registration statements would be established at the time of such offerings.

LOSS PER COMMON SHARE	3 Months Ended
LOSS PER COMMON SHARE	Mar. 31, 2018
Earnings Per Share [Abstract]
LOSS PER COMMON SHARE	9. LOSS PER COMMON SHARE Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. The Company’s potentially dilutive shares, which include outstanding stock options, unvested RSUs, and shares issuable upon conversion of the 2024 Notes, are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. For the three months ended March 31, 2018 and March 31, 2017, the Company realized a net loss of $41.8 million and $78.3 million, respectively. Stock options, unvested RSUs and PRSUs of approximately 7.9 million and 7.1 million shares of common stock were excluded from the calculation of diluted net loss per shares, due to their anti-dilutive effect, as of March 31, 2018 and 2017, respectively. In May 2017, the Company issued $517.5 million of convertible debt pursuant to the 2024 Notes, which under certain circumstances may convert to common shares outstanding. If converted, this $517.5 million of convertible debt would represent approximately 6.8 million common shares. See Note 5, Convertible Senior Notes, for additional information. As provided by the terms of the indenture underlying the 2024 Notes, the Company has a choice to settle the conversion obligation for the 2024 Notes in cash, shares or any combination of cash and shares. The Company currently intends to settle the par value of the 2024 Notes in cash and any excess conversion premium in shares. Accordingly, the par value of the 2024 Notes will not be included in the calculation of diluted income per share, but the dilutive effect of the conversion premium, if any, will be considered in the calculation of diluted net income per share using the treasury stock method.

BIAL AGREEMENT	3 Months Ended
BIAL AGREEMENT	Mar. 31, 2018
Text Block [Abstract]
BIAL AGREEMENT	10. BIAL AGREEMENT In February 2017, the Company entered into an exclusive license agreement with BIAL – Portela & CA, S.A. (BIAL) for the development and commercialization of opicapone for the treatment of human diseases and conditions, including Parkinson’s disease, in the United States and Canada. Under the terms of the agreement, the Company is responsible for the management and cost of all opicapone development and commercialization activities in the United States and Canada. Under the terms of the agreement, the Company paid BIAL an upfront license fee of $30 million, which was expensed in the first quarter of 2017 as in process research and development. In addition, during the first quarter of 2018, the FDA provided guidance on the regulatory path forward to support an NDA for opicapone for Parkinson’s Disease, in which the FDA did not request that the Company conduct an additional Phase III study, resulting in a $10 million event-based milestone payment to BIAL. The Company may also be required to pay up to an additional $105 million in milestone payments associated with the regulatory approval and net sales of products containing opicapone. Prior to FDA approval of opicapone, the Company may be required to pay up to an additional $10 million in milestones based on certain regulatory and clinical results and FDA acceptance of the Company’s NDA submission for opicapone. Upon commercialization of opicapone, the Company has agreed to determine certain annual sales forecasts. In the event that the Company fails to meet the minimum sales requirements for a particular year, the Company will be required to pay BIAL an amount corresponding to the difference between the actual net sales and the minimum sales requirements for such year, and if the Company fails to meet the minimum sales requirements for any two years, BIAL may terminate the agreement. The agreement, unless terminated earlier, will continue on a licensed product-by-licensed product and country-by-country basis until a generic product in respect of such licensed product under the agreement is sold in a country and sales of such generic product are greater than a specified percentage of total sales of such licensed product in such country. Upon the Company’s written request prior to the estimated expiration of the term in respect of a licensed product, the parties shall negotiate a good faith continuation of BIAL’s supply of such licensed product after the term. After the term, and if BIAL is not supplying a certain licensed product, the Company shall pay BIAL a trademark royalty based on the net sales of such licensed product. Either party may terminate the agreement earlier if the other party materially breaches the agreement and does not cure the breach within a specified notice period, or upon the other party’s insolvency. BIAL may terminate the agreement if the Company fails to use commercially reasonable efforts or fails to submit an NDA for a licensed product by a specified date or under certain circumstances involving a change of control of the Company. In certain circumstances where BIAL elects to terminate the agreement in connection with the Company’s change of control, BIAL shall pay the Company a termination fee. The Company may terminate the agreement at any time for any reason upon six months written notice to BIAL if prior to the first NDA approval in the United States, and upon nine months written notice to BIAL if such notice is given after the first NDA approval in the United States. If the Company’s termination request occurs prior to the first NDA approval in the United States, the Company will have to pay BIAL a termination fee except under certain conditions specified in the agreement.

COMMITMENTS AND CONTINGENCIES	3 Months Ended
COMMITMENTS AND CONTINGENCIES	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	11. COMMITMENTS AND CONTINGENCIES From time to time, the Company may be subject to legal proceedings and claims in the ordinary course of business. On December 1, 2015, Icahn School of Medicine at Mount Sinai (Mount Sinai) filed a complaint against the Company in the United States District Court for the Southern District of New York: Icahn School of Medicine at Mount Sinai v. Neurocrine Biosciences, Inc., Case No. 1:15-cv-09414. In the complaint, Mount Sinai alleges that the Company, by entering into an exclusive worldwide collaboration with AbbVie to develop and commercialize next-generation GnRH antagonists, breached a license agreement with Mount Sinai dated August 27, 1999. Mount Sinai is seeking unspecified monetary damages, future sublicensing fees and attorney’s fees. In January 2016, the Company filed a motion to dismiss this complaint in its entirety. In June 2016, the Court denied the motion in part and granted the motion in part, ruling that while Mount Sinai could continue its lawsuit against the Company, there was no requirement by the Company to obtain Mount Sinai’s consent prior to licensing the next-generation GnRH antagonists to AbbVie. In July 2016, the Company filed its answer denying Mount Sinai’s allegations, and filed counterclaims against Mount Sinai. Mount Sinai filed a motion to dismiss the Company’s counterclaims and affirmative defenses, which the Court granted. A trial is anticipated to occur in the third quarter of 2018. The Company believes that it has meritorious defenses to the claims made in the complaint and intends to vigorously defend against such claims, but is not able to predict the ultimate outcome of this action, or estimate any potential loss. The Company is not aware of any other proceedings or claims that it believes will have, individually or in the aggregate, a material adverse effect on its business, financial condition or results of operations.

Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($)	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017
Organization And Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 4,500,000		$ 4,500,000
Topic 606
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings		$ 0
ASU 2016-18
Organization And Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 4,500,000			$ 5,100,000

Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Investments [Line Items]
Investments	$ 561,487	$ 508,578
Commercial paper
Schedule Of Investments [Line Items]
Investments	41,993	75,362
Corporate debt securities
Schedule Of Investments [Line Items]
Investments	501,103	414,815
Domestic and foreign government agencies debt securities
Schedule Of Investments [Line Items]
Investments	$ 18,391	$ 18,401

Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	$ 534,736	$ 460,252
Less Than 12 Months, Unrealized Losses	(3,618)	(1,777)
12 Months or Greater, Estimated Fair Value	26,751	35,566
12 Months or Greater, Unrealized Losses	(79)	(74)
Total Estimated Fair Value	561,487	495,818
Total Unrealized Losses	(3,697)	(1,851)
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	41,993	62,602
Less Than 12 Months, Unrealized Losses	(112)	(35)
12 Months or Greater, Estimated Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total Estimated Fair Value	41,993	62,602
Total Unrealized Losses	(112)	(35)
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	481,836	386,728
Less Than 12 Months, Unrealized Losses	(3,409)	(1,660)
12 Months or Greater, Estimated Fair Value	19,267	28,087
12 Months or Greater, Unrealized Losses	(62)	(50)
Total Estimated Fair Value	501,103	414,815
Total Unrealized Losses	(3,471)	(1,710)
Domestic and foreign government agencies debt securities
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	10,907	10,922
Less Than 12 Months, Unrealized Losses	(97)	(82)
12 Months or Greater, Estimated Fair Value	7,484	7,479
12 Months or Greater, Unrealized Losses	(17)	(24)
Total Estimated Fair Value	18,391	18,401
Total Unrealized Losses	$ (114)	$ (106)

Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	$ 561.5	$ 508.6
Short-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	460.5	516.0
Short-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	147.4	170.2
Short-term investments \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	69.9	159.9
Short-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	7.5	7.5
Short-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	235.7	178.4
Long-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	1.5	1.5
Long-term investments \| Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	3.0	3.0
Long-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	10.9	10.9
Long-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	265.4	236.4
Investments Including Cash Equivalents And Restricted Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	741.3	767.8
Cash and Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Carrying Value	179.8	259.2
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.1
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Short-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	147.4	170.2
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Short-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	147.4	170.2
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Short-term investments \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Short-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Short-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Long-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	1.5	1.5
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Long-term investments \| Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	3.0	3.0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Long-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Long-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Investments Including Cash Equivalents And Restricted Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	151.9	174.7
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Cash and Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	151.9	174.6
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	561.5	508.5
Significant Other Observable Inputs (Level 2) \| Short-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	313.1	345.8
Significant Other Observable Inputs (Level 2) \| Short-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Other Observable Inputs (Level 2) \| Short-term investments \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	69.9	159.9
Significant Other Observable Inputs (Level 2) \| Short-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	7.5	7.5
Significant Other Observable Inputs (Level 2) \| Short-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	235.7	178.4
Significant Other Observable Inputs (Level 2) \| Long-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Other Observable Inputs (Level 2) \| Long-term investments \| Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Other Observable Inputs (Level 2) \| Long-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	10.9	10.9
Significant Other Observable Inputs (Level 2) \| Long-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	265.4	236.4
Significant Other Observable Inputs (Level 2) \| Investments Including Cash Equivalents And Restricted Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	589.4	593.1
Significant Other Observable Inputs (Level 2) \| Cash and Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	27.9	84.6
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Short-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Short-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Short-term investments \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Short-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Short-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Long-term investments \| Cash and money market fund
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Long-term investments \| Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Long-term investments \| Domestic and foreign government agencies debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Long-term investments \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Investments Including Cash Equivalents And Restricted Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Cash and Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets on recurring basis	$ 0.0	$ 0.0

Convertible Senior Notes - Debt Net of Discount and Deferred Financing (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Principal	$ 517,500	$ 517,500
Deferred financing costs	(9,326)	(9,652)
Debt discount, net	(133,965)	(138,230)
Net carrying amount	$ 374,209	$ 369,618

Compensation Expense Related to Share-Based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 19,879	$ 8,976
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	7,256	5,453
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 12,623	$ 3,523

Stockholders' Equity - Additional Information (Detail)	3 Months Ended
Stockholders' Equity - Additional Information (Detail)	Mar. 31, 2018 shares
February Two Thousand Seventeen Shelf Registration [Member]
Class of Stock [Line Items]
Number of securities sold	0

Loss Per Common Share - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions		3 Months Ended
	May 02, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Loss Per Common Share [Line Items]
Net loss		$ (41,818)	$ (78,326)
Convertible senior notes principal amount		$ 517,500		$ 517,500
2.25% Convertible Senior Notes due 2024
Loss Per Common Share [Line Items]
Common share equivalents excluded from computation of earnings per share	6.8
Convertible senior notes principal amount	$ 517,500
Stock options, Unvested RSUs and PRSUs
Loss Per Common Share [Line Items]
Common share equivalents excluded from computation of earnings per share		7.9	7.1

BIAL Agreement - Additional Information (Detail) - B I A L - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
License Agreement [Line Items]
License agreement date	Feb. 09, 2017
Up-front license fees		$ (30)
Event Based Milestones
License Agreement [Line Items]
Milestone payables	$ 10
Regulatory Approval and Net Sales Milestones
License Agreement [Line Items]
Milestone payables	105
Regulatory and Clinical Results and FDA Acceptance Milestones
License Agreement [Line Items]
Milestone payables	$ 10