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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	ACAD
Entity Registrant Name	ACADIA PHARMACEUTICALS INC
Entity Central Index Key	0001070494
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		124,205,637

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 112,616	$ 163,620
Investment securities, available-for-sale	254,009	365,416
Accounts receivable, net	14,221	5,903
Interest and other receivables	1,033	1,237
Inventory	5,536	4,175
Prepaid expenses	14,557	7,546
Total current assets	401,972	547,897
Property and equipment, net	2,991	3,081
Intangible assets, net	5,907	7,015
Restricted cash	2,475	2,375
Other assets	369	785
Total assets	413,714	561,153
Liabilities and stockholders’ equity
Accounts payable	2,962	3,912
Accrued liabilities	33,181	36,029
Deferred revenue		2,644
Total current liabilities	36,143	42,585
Long-term liabilities	245	157
Total liabilities	36,388	42,742
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at September 30, 2017 and December 31, 2016; no shares issued and outstanding at September 30, 2017 and December 31, 2016
Common stock, $0.0001 par value; 225,000,000 shares authorized at September 30, 2017 and December 31, 2016; 122,717,018 shares and 121,367,169 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	12	12
Additional paid-in capital	1,532,188	1,452,272
Accumulated deficit	(1,154,801)	(933,979)
Accumulated other comprehensive (loss) income	(73)	106
Total stockholders’ equity	377,326	518,411
Total liabilities and stockholders’ equity	$ 413,714	$ 561,153

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
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	$ 0.0001	$ 0.0001
Common stock, shares authorized	225,000,000	225,000,000
Common stock, shares issued	122,717,018	121,367,169
Common stock, shares outstanding	122,717,018	121,367,169

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Product sales, net	$ 35,578	$ 5,268	$ 81,339	$ 5,365
Collaborative revenue				4
Total revenues	35,578	5,268	81,339	5,369
Operating expenses
Cost of product sales	2,135	845	6,622	1,371
License fees and royalties	1,078	475	2,735	723
Research and development	36,421	25,813	106,010	69,066
Selling, general and administrative	62,255	50,534	189,523	128,793
Total operating expenses	101,889	77,667	304,890	199,953
Loss from operations	(66,311)	(72,399)	(223,551)	(194,584)
Interest income, net	1,063	786	3,019	1,887
Net loss	$ (65,248)	$ (71,613)	$ (220,532)	$ (192,697)
Net loss per common share, basic and diluted	$ (0.53)	$ (0.61)	$ (1.81)	$ (1.69)
Weighted average common shares outstanding, basic and diluted	122,484	117,497	122,089	114,063

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (65,248)	$ (71,613)	$ (220,532)	$ (192,697)
Other comprehensive gain (loss):
Unrealized gain (loss) on investment securities	25	328	(174)	524
Foreign currency translation adjustments	(1)	(1)	(5)	(2)
Comprehensive loss	$ (65,224)	$ (71,286)	$ (220,711)	$ (192,175)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (220,532)	$ (192,697)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	53,513	39,847
Amortization of premiums and accretion of discounts on investment securities	(138)	145
Amortization of intangible assets	1,108	615
Depreciation	904	583
Loss on disposal of assets		5
Changes in operating assets and liabilities:
Accounts receivable, net	(8,318)	(3,839)
Interest and other receivables	204	253
Inventory	(1,645)	(3,503)
Prepaid expenses and other current assets	(7,011)	(2,887)
Restricted cash	(100)	(2,000)
Other assets	416	(646)
Accounts payable	(950)	994
Accrued liabilities	(2,857)	14,090
Deferred revenue	(2,644)	1,876
Long-term liabilities	88	(55)
Net cash used in operating activities	(187,962)	(147,219)
Cash flows from investing activities
Purchases of investment securities	(353,840)	(592,868)
Maturities of investment securities	465,211	271,061
Intangible assets		(8,000)
Purchases of property and equipment	(805)	(1,257)
Net cash provided by (used in) investing activities	110,566	(331,064)
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	26,397	515,506
Proceeds from settlement agreement		14,320
Net cash provided by financing activities	26,397	529,826
Effect of exchange rate changes on cash	(5)	(2)
Net (decrease) increase in cash and cash equivalents	(51,004)	51,541
Cash and cash equivalents
Beginning of period	163,620	102,138
End of period	112,616	153,679
Supplemental disclosure of noncash information:
Property and equipment purchases in accounts payable and accrued liabilities	9	287
Stock-based compensation capitalized in inventory	$ 284	$ 798

Organization and Business	9 Months Ended
Organization and Business	Sep. 30, 2017
Accounting Policies [Abstract]
Organization and Business	1. Organization and Business ACADIA Pharmaceuticals Inc. (the “Company”), based in San Diego, California, is a biopharmaceutical company focused on the development and commercialization of innovative medicines to address unmet medical needs in central nervous system disorders. The Company was originally incorporated in Vermont in 1993 as Receptor Technologies, Inc. and reincorporated in Delaware in 1997. On April 29, 2016, the U.S. Food and Drug Administration (“FDA”) approved the Company’s first drug, NUPLAZID^® (pimavanserin), for the treatment of hallucinations and delusions associated with Parkinson’s disease psychosis (“PD Psychosis”). NUPLAZID became available for prescription in the United States on May 31, 2016.

Basis of Presentation and Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	2. Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements of the Company should be read in conjunction with the audited financial statements and notes thereto as of and for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K (“Annual Report”) filed with the Securities and Exchange Commission (the “SEC”). The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying financial statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying financial statements reflect all adjustments (consisting of normal recurring adjustments) that are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. Actual results could differ from those estimates. Accounts Receivable Accounts receivable are recorded net of customer allowances for distribution fees, prompt payment discounts, chargebacks, and doubtful accounts. Allowances for distribution fees, prompt payment discounts and chargebacks are based on contractual terms. The Company estimates the allowance for doubtful accounts based on existing contractual payment terms, actual payment patterns of its customers and individual customer circumstances. At September 30, 2017, the Company determined that an allowance for doubtful accounts was not required. No accounts were written off during the periods presented. License Fees and Royalties The Company expenses amounts paid to acquire licenses associated with products under development when the ultimate recoverability of the amounts paid is uncertain and the technology has no alternative future use when acquired. Acquisitions of technology licenses are charged to expense or capitalized based upon management’s assessment regarding the ultimate recoverability of the amounts paid and the potential for alternative future use. The Company has determined that technological feasibility for its product candidates is reached when the requisite regulatory approvals are obtained to make the product available for sale. In connection with the FDA approval of NUPLAZID in April 2016, the Company made a one-time milestone payment of $8.0 million pursuant to its 2006 license agreement with the Ipsen Group in which the Company licensed certain intellectual property rights that complement its patent portfolio for its serotonin platform, including NUPLAZID. The Company capitalized the $8.0 million payment as an intangible asset and is amortizing the asset on a straight-line basis over the estimated useful life of the licensed patents through the second half of 2021. The Company recorded amortization expense related to its intangible asset of $0.4 million and $1.1 million for the three and nine months ended September 30, 2017, respectively. As of September 30, 2017, estimated future amortization expense related to the Company’s intangible asset was $0.4 million for the remainder of 2017, $1.5 million for each of 2018, 2019, and 2020, and $1.0 million for 2021. Royalties incurred in connection with the Company’s license agreement with the Ipsen Group, as disclosed in Note 9, are expensed to license fees and royalties as revenue from product sales is recognized. Revenue Recognition Product Sales, Net The Company’s net product sales consist of U.S. sales of NUPLAZID and are recognized when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred and title to the product and associated risk of loss has passed to the customer, (iii) the price is fixed or determinable, and (iv) collectability is reasonably assured. NUPLAZID was approved by the FDA on April 29, 2016 and the Company commenced shipments of NUPLAZID to specialty pharmacies (“SPs”) and specialty distributors (“SDs”) in late May 2016. Prior to April 1, 2017, the Company deferred sales of NUPLAZID and recognized revenue when an SP dispensed product to a patient based on the fulfillment of a prescription and when an SD sold product to a government facility, long-term care pharmacy, or in-patient hospital pharmacy. In the second quarter of 2017 the Company determined that it had sufficient volume of activity to reasonably estimate its allowances for rebates and chargebacks and began recognizing NUPLAZID revenue, net of estimated allowances for rebates, price adjustments, returns, chargebacks, and prompt payment discounts, at the point of sale to the SPs and SDs which is commonly referred to as the “sell-in” revenue recognition model. As a result, the Company recorded a one-time adjustment during the three months ended June 30, 2017, to recognize deferred revenue on previously shipped product. This adjustment had no impact on net revenues for the three months ended September 30, 2017. The effect on income from operations and on net income is that the Company is able to recognize revenue earlier on this sell-in method, net of a provision for estimated allowances, since the Company can record revenue once sold to the SP or SD rather than waiting until the product is sold to the end user on a sell-through basis, which it had done for periods prior to April 1, 2017. Product shipping and handling costs are included in cost of product sales. The Company recognizes revenue from product sales net of the following allowances and reflects each of these as either a reduction to the related accounts receivable or as an accrued liability, depending on how the amount is settled: Distribution Fees: Distribution fees include distribution service fees paid to the SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (“WAC”), fees for data, and prompt payment discounts. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized. Rebates: Allowances for rebates include mandated discounts under the Medicaid Drug Rebate Program and the Medicare Part D prescription drug benefit. Rebates are amounts owed after the final dispensing of the product to a benefit plan participant and are based upon contractual agreements with, or statutory requirements pertaining to, Medicaid and Medicare benefit providers. The allowance for rebates is based on statutory discount rates and expected utilization. The Company’s estimates for expected utilization of rebates is based on historical data received from the SPs and SDs since product launch. Rebates are generally invoiced and paid in arrears so that the accrual balance consists of an estimate of the amount expected to be incurred for the current quarter’s activity, plus an accrual balance for prior quarters’ unpaid rebates. If actual future rebates vary from estimates, the Company may need to adjust prior period accruals, which would affect revenue in the period of adjustment. Chargebacks: Chargebacks are discounts and fees that relate to contracts with government and other entities purchasing from the SDs at a discounted price. The SDs charge back to the Company the difference between the price initially paid by the SDs and the discounted price paid to the SDs by these entities. The Company also incurs group purchasing organization fees for transactions through certain purchasing organizations. The Company estimates sales with these entities and accrues for anticipated chargebacks and organization fees, based on the applicable contractual terms. If actual future chargebacks vary from these estimates, the Company may need to adjust prior period accruals, which would affect revenue in the period of adjustment. Co-Payment Assistance: The Company offers co-payment assistance to commercially insured patients meeting certain eligibility requirements. Co-payment assistance is accrued for based on actual program participation and estimates of program redemption using data provided by third-party administrators. Product Returns: Consistent with industry practice, the Company offers the SPs and SDs limited product return rights for damages, shipment errors, and expiring product; provided that the return is within a specified period around the product expiration 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. As the Company receives inventory reports from the SPs and SDs and has the ability to control the amount of product that is sold to the SPs and SDs, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from the SPs and SDs. In arriving at its estimate, the Company also considers historical product returns, the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.

Net Loss Per Share	9 Months Ended
Net Loss Per Share	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss Per Share	3. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common stock equivalents outstanding for the period determined using the treasury stock method. For purposes of this calculation, stock options, employee stock purchase plan rights, and warrants are considered to be common stock equivalents but are not included in the calculations of diluted net loss per share for the periods presented as their effect would be anti-dilutive. The Company incurred net losses for all periods presented and there were no reconciling items for potentially dilutive securities. More specifically, at September 30, 2017 and 2016, stock options, employee stock purchase plan rights, and warrants totaling approximately 20,154,000 shares and 14,463,000 shares, respectively, were excluded from the calculation of diluted net loss per share as their effect would have been anti-dilutive.

Stock-Based Compensation

9 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

4. Stock-Based Compensation

The following table summarizes the total stock-based compensation expense included in the Company’s statements of operations for the periods presented (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Cost of product sales	$	1,210	$	308	$	2,971	$	497
Research and development		6,877		4,319		18,598		13,495
Selling, general and administrative		11,611		9,382		31,944		25,855
	$	19,698	$	14,009	$	53,513	$	39,847

Balance Sheet Details

9 Months Ended

Sep. 30, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Details

5. Balance Sheet Details

Inventory consisted of the following (in thousands):

	September 30, 2017		December 31, 2016
Raw material	$	4,088	$	1,820
Finished goods		1,448		2,355
	$	5,536	$	4,175

Accrued liabilities consisted of the following (in thousands):

	September 30, 2017		December 31, 2016
Accrued compensation and benefits	$	14,192	$	14,382
Accrued consulting and professional fees		7,183		9,488
Accrued research and development services		5,681		8,551
Accrued sales allowances		3,721		1,999
Other		2,404		1,609
	$	33,181	$	36,029

Investment Securities

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Investment Securities

6. Investment Securities

Investment securities, all classified as available-for-sale, consisted of the following (in thousands):

	September 30, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	66,319	$	1	$	(13	)	$	66,307
Government sponsored enterprise securities		35,711		—		(5	)		35,706
Corporate debt securities		61,966		—		(38	)		61,928
Commercial paper		90,095		—		(27	)		90,068
	$	254,091	$	1	$	(83	)	$	254,009

	December 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	82,484	$	6	$	(3	)	$	82,487
Government sponsored enterprise securities		73,789		1		(5	)		73,785
Corporate debt securities		79,190		—		(72	)		79,118
Commercial paper		129,861		165		—			130,026
	$	365,324	$	172	$	(80	)	$	365,416

At each reporting date, the Company performs an evaluation of impairment to determine if any unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, and the Company’s intent and ability to hold the investment until recovery of its amortized cost basis. The Company intends, and has the ability, to hold its investments in unrealized loss positions until their amortized cost basis has been recovered. Based on its evaluation, the Company determined that its unrealized losses were not other-than-temporary at September 30, 2017 and December 31, 2016.

The Company has classified all of its available-for-sale investment securities, including those with maturities beyond one year, as current assets on its consolidated balance sheets based on the highly liquid nature of the investment securities and because these investment securities are considered available for use in current operations. As of September 30, 2017, the Company held $10.9 million of available-for-sale investment securities with contractual maturity dates more than one year and less than two years. No securities with similar maturity dates were held as of December 31, 2016.

Fair Value Measurements

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

7. Fair Value Measurements

The Company’s investments include cash equivalents and available-for-sale investment securities consisting of a money market fund, U.S. Treasury notes, and high quality, marketable debt instruments of corporations and government sponsored enterprises in accordance with the Company’s investment policy. The Company’s investment policy defines allowable investments and establishes guidelines relating to credit quality, diversification, and maturities of its investments to preserve principal and maintain liquidity. All investment securities have a credit rating of at least A3/A- or better, or P-1/A-1 or better, as determined by Moody’s Investors Service or Standard & Poor’s.

The Company’s cash equivalents and available-for-sale investment securities are classified within the fair value hierarchy as defined by authoritative guidance. The Company’s investment securities classified as Level 1 are valued using quoted market prices. The Company obtains the fair value of its Level 2 financial instruments from third party pricing services. The pricing services utilize industry standard valuation models whereby all significant inputs, including benchmark yields, reported trades, broker/dealer quotes, issuer spreads, bids, offers, or other market-related data, are observable. The Company validates the prices provided by the third-party pricing services by reviewing their pricing methods and matrices, and obtaining market values from other pricing sources. After completing the validation procedures, the Company did not adjust or override any fair value measurements provided by these pricing services as of September 30, 2017 and December 31, 2016.

The Company does not hold any securities classified as Level 3, which are securities valued using unobservable inputs. The Company has not transferred any investment securities between the classification levels.

The recurring fair value measurements of the Company’s cash equivalents and available-for-sale investment securities at September 30, 2017 and December 31, 2016 consisted of the following (in thousands):

			Fair Value Measurements at Reporting Date Using
	September 30, 2017		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	44,411	$	44,411	$	—	$	—
U.S. Treasury notes		66,307	$	66,307		—		—
Government sponsored enterprise securities		65,685		—		65,685		—
Corporate debt securities		78,942		—		78,942		—
Commercial paper		110,050		—		110,050		—
	$	365,395	$	110,718	$	254,677	$	—

			Fair Value Measurements at Reporting Date Using
	December 31, 2016		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	129,292	$	129,292	$	—	$	—
U.S. Treasury notes		82,487		82,487		—		—
Government sponsored enterprise securities		88,773		—		88,773		—
Corporate debt securities		82,857		—		82,857		—
Commercial paper		140,024		—		140,024		—
	$	523,433	$	211,779	$	311,654	$	—

- 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

Stockholders' Equity	9 Months Ended
Stockholders' Equity	Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Public Offerings In August 2016, the Company raised net proceeds of approximately $215.9 million from the sale of 6,969,696 shares of its common stock in a follow-on public offering, including 909,090 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares. In January 2016, the Company raised net proceeds of approximately $281.6 million from the sale of 10,344,827 shares of its common stock in a follow-on public offering. In connection with the January 2016 offering, the Company entered into a registration rights agreement (the “Registration Rights Agreement”) with 667, L.P., Baker Brothers Life Sciences, L.P. and 14159, L.P. (the “Baker Entities”), all of which are existing stockholders of the Company and are affiliated with two of its directors, Julian C. Baker and Dr. Stephen R. Biggar. Under the Registration Rights Agreement, the Company agreed that, if the Baker Entities demand that the Company register their shares of its common stock, par value $0.0001 per share, for resale under the Securities Act of 1933, as amended (the “Securities Act”), the Company would be obligated to effect such registration. The Company’s registration obligations under the Registration Rights Agreement cover all shares of its common stock then held or later acquired by the Baker Entities (including approximately $75.0 million and $43.0 million of shares that the Baker Entities purchased at the public offering price in the January 2016 and August 2016 offerings, respectively), will continue in effect for up to 10 years, and include the Company’s obligation to facilitate certain underwritten public offerings of its common stock by the Baker Entities in the future. The Company has agreed to bear all expenses incurred by it in effecting any registration pursuant to the Registration Rights Agreement as well as the legal expenses of the Baker Entities of up to $50,000 per underwritten public offering effected pursuant to the Registration Rights Agreement. On April 1, 2016, pursuant to the Registration Rights Agreement, the Company filed a registration statement covering all shares owned by the Baker Entities as of March 31, 2016.

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Royalty Payments Pursuant to the terms of its 2006 license agreement with the Ipsen Group, the Company is required to make royalty payments of two percent of net sales of NUPLAZID. Corporate Credit Card Program In connection with the Company’s credit card program, the Company established a letter of credit in 2016 for $2.0 million, which has automatic annual extensions and is fully secured by restricted cash. Legal Proceedings In March 2015, following the Company’s announcement of the update to the timing of its planned NDA submission to the FDA for NUPLAZID for the treatment of PD Psychosis and the subsequent decline of the price of its common stock, two putative securities class action complaints (captioned Rihn v. ACADIA Pharmaceuticals Inc., Case No. 15-cv-0575-BTM-DHB, and Wright v. ACADIA Pharmaceuticals Inc., Case No. 15-cv-0593- BTM-DHB) were filed in the U.S. District Court for the Southern District of California (the “Court”) against the Company and certain of its current and former officers. The complaints generally alleged that the defendants violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 by making materially false and misleading statements regarding the timing of the Company’s planned NDA submission to the FDA for NUPLAZID, thereby artificially inflating the price of its common stock. The complaints sought unspecified monetary damages and other relief. On April 10 and June 1, 2015, the Court entered orders deferring the defendants’ response to the Rihn and Wright complaints until after the Court appointed a lead plaintiff and assigned lead counsel. On May 12, 2015, several putative stockholders filed separate motions to consolidate the two actions and be appointed lead plaintiff. On September 8, 2015, the Court issued an order consolidating the two actions, appointing lead plaintiff, and assigning lead counsel. On November 16, 2015, lead plaintiff filed a consolidated complaint with the Court which, like the prior complaints, accuses the defendants of making materially false and misleading statements regarding the anticipated timing of the Company’s planned NDA submission to the FDA for NUPLAZID. On January 15, 2016, the defendants filed a motion to dismiss the consolidated complaint. On September 19, 2016, the Court issued an order denying the motion to dismiss the consolidated complaint. On March 13, 2017, the parties signed a Stipulation of Settlement setting forth the terms of the proposed settlement. On June 9, 2017, the Court preliminarily approved the settlement (the “Preliminary Approval Order”). Among other things, the Preliminary Approval Order set an opt-out deadline of August 29, 2017; an objection deadline of September 13, 2017; and a final approval hearing for October 3, 2017. On October 3, 2017, the Court continued the hearing so that, among other things, lead plaintiff could submit additional documents in support of final approval. The Court has set January 8, 2018 as the date for the continued final approval hearing.

Recent Accounting Pronouncements	9 Months Ended
Recent Accounting Pronouncements	Sep. 30, 2017
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Recent Accounting Pronouncements	10. Recent Accounting Pronouncements In November 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-18, Statement of Cash Flows: Restricted Cash, which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included within cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. This guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted. The Company expects to adopt this standard on January 1, 2018. The adoption of this ASU will modify the Company’s current classification within the consolidated statement of cash flows but is not expected to materially impact the Company’s consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments, which changes the impairment model for most financial assets and certain other instruments. For trade receivables and other instruments, entities will be required to use a new forward-looking expected loss model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses will be recognized as allowances rather than as reductions in the amortized cost of the securities. This guidance is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those years, with early adoption permitted only as of annual reporting periods beginning after December 15, 2018. The Company is currently evaluating the timing and impact of the adoption of this guidance on the Company’s consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation: Improvements to Employee Share-Based Payment Accounting, which is intended to simplify several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, classification on the statement of cash flows, and accounting for forfeitures. This guidance was effective for annual reporting periods beginning after December 15, 2016, including interim periods within those years. The Company adopted this guidance in the first quarter of 2017 using the modified retrospective transition method. Accordingly, the Company increased its deferred tax assets by $36.8 million, with a corresponding increase to its valuation allowance, to record previously unrecognized excess tax benefits. Additionally, the Company elected to make an accounting policy change to recognize forfeitures as they occur. As a result, the Company recorded an increase to additional paid-in capital and a corresponding increase to accumulated deficit of $0.3 million, respectively, to reflect the incremental stock-based compensation expense that would have been recognized in prior years pursuant to the modified guidance. Additionally, the Company increased its deferred tax assets by $0.1 million, with a corresponding increase to its valuation allowance, to record the excess tax benefit from the change. In February 2016, the FASB issued ASU 2016-02, Leases, which requires a lessee to recognize a lease liability and a right-of-use asset for all leases with lease terms of more than 12 months. This guidance is effective for annual reporting periods beginning after December 15, 2018, including interim periods within those years, and early adoption is permitted. Companies are required to adopt this guidance using a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. While the Company is still evaluating the timing and impact of the adoption of this guidance on its consolidated financial statements, it anticipates that the adoption could result in an increase in the assets and liabilities recorded on its consolidated balance sheet. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers, which supersedes nearly all existing revenue recognition guidance under generally accepted accounting principles. This ASU, as amended, is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. This ASU also requires additional disclosure about the nature, amount, timing, and uncertainty of revenue and cash flows arising from customer contracts. The original guidance was effective for annual reporting periods beginning after December 15, 2016. However, in July 2015, the FASB agreed to delay the effective date by one year, with early adoption permitted, but not before the original effective date of the standard. Companies may use either a full retrospective or a modified retrospective approach to adopt this guidance. The Company anticipates adopting ASU 2014-09 on January 1, 2018 using the modified-retrospective approach. At present, the Company has one source of revenue: the sale of NUPLAZID to its customers. The Company’s evaluation of the customer contracts governing these sales is still underway. However, recognition of the Company’s revenue under the new standard is expected to be materially consistent with the Company’s current revenue recognition policy, which uses the sell-in method. The new standard is not expected to materially impact the timing or amounts of revenue recognized.

Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of the Company should be read in conjunction with the audited financial statements and notes thereto as of and for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K (“Annual Report”) filed with the Securities and Exchange Commission (the “SEC”). The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying financial statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying financial statements reflect all adjustments (consisting of normal recurring adjustments) that are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. Actual results could differ from those estimates.
Accounts Receivable	Accounts Receivable Accounts receivable are recorded net of customer allowances for distribution fees, prompt payment discounts, chargebacks, and doubtful accounts. Allowances for distribution fees, prompt payment discounts and chargebacks are based on contractual terms. The Company estimates the allowance for doubtful accounts based on existing contractual payment terms, actual payment patterns of its customers and individual customer circumstances. At September 30, 2017, the Company determined that an allowance for doubtful accounts was not required. No accounts were written off during the periods presented.
License Fees and Royalties	License Fees and Royalties The Company expenses amounts paid to acquire licenses associated with products under development when the ultimate recoverability of the amounts paid is uncertain and the technology has no alternative future use when acquired. Acquisitions of technology licenses are charged to expense or capitalized based upon management’s assessment regarding the ultimate recoverability of the amounts paid and the potential for alternative future use. The Company has determined that technological feasibility for its product candidates is reached when the requisite regulatory approvals are obtained to make the product available for sale. In connection with the FDA approval of NUPLAZID in April 2016, the Company made a one-time milestone payment of $8.0 million pursuant to its 2006 license agreement with the Ipsen Group in which the Company licensed certain intellectual property rights that complement its patent portfolio for its serotonin platform, including NUPLAZID. The Company capitalized the $8.0 million payment as an intangible asset and is amortizing the asset on a straight-line basis over the estimated useful life of the licensed patents through the second half of 2021. The Company recorded amortization expense related to its intangible asset of $0.4 million and $1.1 million for the three and nine months ended September 30, 2017, respectively. As of September 30, 2017, estimated future amortization expense related to the Company’s intangible asset was $0.4 million for the remainder of 2017, $1.5 million for each of 2018, 2019, and 2020, and $1.0 million for 2021. Royalties incurred in connection with the Company’s license agreement with the Ipsen Group, as disclosed in Note 9, are expensed to license fees and royalties as revenue from product sales is recognized.
Revenue Recognition	Revenue Recognition Product Sales, Net The Company’s net product sales consist of U.S. sales of NUPLAZID and are recognized when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred and title to the product and associated risk of loss has passed to the customer, (iii) the price is fixed or determinable, and (iv) collectability is reasonably assured. NUPLAZID was approved by the FDA on April 29, 2016 and the Company commenced shipments of NUPLAZID to specialty pharmacies (“SPs”) and specialty distributors (“SDs”) in late May 2016. Prior to April 1, 2017, the Company deferred sales of NUPLAZID and recognized revenue when an SP dispensed product to a patient based on the fulfillment of a prescription and when an SD sold product to a government facility, long-term care pharmacy, or in-patient hospital pharmacy. In the second quarter of 2017 the Company determined that it had sufficient volume of activity to reasonably estimate its allowances for rebates and chargebacks and began recognizing NUPLAZID revenue, net of estimated allowances for rebates, price adjustments, returns, chargebacks, and prompt payment discounts, at the point of sale to the SPs and SDs which is commonly referred to as the “sell-in” revenue recognition model. As a result, the Company recorded a one-time adjustment during the three months ended June 30, 2017, to recognize deferred revenue on previously shipped product. This adjustment had no impact on net revenues for the three months ended September 30, 2017. The effect on income from operations and on net income is that the Company is able to recognize revenue earlier on this sell-in method, net of a provision for estimated allowances, since the Company can record revenue once sold to the SP or SD rather than waiting until the product is sold to the end user on a sell-through basis, which it had done for periods prior to April 1, 2017. Product shipping and handling costs are included in cost of product sales. The Company recognizes revenue from product sales net of the following allowances and reflects each of these as either a reduction to the related accounts receivable or as an accrued liability, depending on how the amount is settled: Distribution Fees: Distribution fees include distribution service fees paid to the SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (“WAC”), fees for data, and prompt payment discounts. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized. Rebates: Allowances for rebates include mandated discounts under the Medicaid Drug Rebate Program and the Medicare Part D prescription drug benefit. Rebates are amounts owed after the final dispensing of the product to a benefit plan participant and are based upon contractual agreements with, or statutory requirements pertaining to, Medicaid and Medicare benefit providers. The allowance for rebates is based on statutory discount rates and expected utilization. The Company’s estimates for expected utilization of rebates is based on historical data received from the SPs and SDs since product launch. Rebates are generally invoiced and paid in arrears so that the accrual balance consists of an estimate of the amount expected to be incurred for the current quarter’s activity, plus an accrual balance for prior quarters’ unpaid rebates. If actual future rebates vary from estimates, the Company may need to adjust prior period accruals, which would affect revenue in the period of adjustment. Chargebacks: Chargebacks are discounts and fees that relate to contracts with government and other entities purchasing from the SDs at a discounted price. The SDs charge back to the Company the difference between the price initially paid by the SDs and the discounted price paid to the SDs by these entities. The Company also incurs group purchasing organization fees for transactions through certain purchasing organizations. The Company estimates sales with these entities and accrues for anticipated chargebacks and organization fees, based on the applicable contractual terms. If actual future chargebacks vary from these estimates, the Company may need to adjust prior period accruals, which would affect revenue in the period of adjustment. Co-Payment Assistance: The Company offers co-payment assistance to commercially insured patients meeting certain eligibility requirements. Co-payment assistance is accrued for based on actual program participation and estimates of program redemption using data provided by third-party administrators. Product Returns: Consistent with industry practice, the Company offers the SPs and SDs limited product return rights for damages, shipment errors, and expiring product; provided that the return is within a specified period around the product expiration 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. As the Company receives inventory reports from the SPs and SDs and has the ability to control the amount of product that is sold to the SPs and SDs, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from the SPs and SDs. In arriving at its estimate, the Company also considers historical product returns, the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.

- Definition

Disclosure of accounting policy for trade and other accounts receivable, and finance, loan and lease receivables, including those classified as held for investment and held for sale. This disclosure may include (1) the basis at which such receivables are carried in the entity's statements of financial position (2) how the level of the valuation allowance for receivables is determined (3) when impairments, charge-offs or recoveries are recognized for such receivables (4) the treatment of origination fees and costs, including the amortization method for net deferred fees or costs (5) the treatment of any premiums or discounts or unearned income (6) the entity's income recognition policies for such receivables, including those that are impaired, past due or placed on nonaccrual status and (7) the treatment of foreclosures or repossessions (8) the nature and amount of any guarantees to repurchase receivables.

+ References + Details

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-based Compensation Expense Included in Statements of Operations

The following table summarizes the total stock-based compensation expense included in the Company’s statements of operations for the periods presented (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Cost of product sales	$	1,210	$	308	$	2,971	$	497
Research and development		6,877		4,319		18,598		13,495
Selling, general and administrative		11,611		9,382		31,944		25,855
	$	19,698	$	14,009	$	53,513	$	39,847

Balance Sheet Details (Tables)

9 Months Ended

Sep. 30, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Inventory

Inventory consisted of the following (in thousands):

	September 30, 2017		December 31, 2016
Raw material	$	4,088	$	1,820
Finished goods		1,448		2,355
	$	5,536	$	4,175

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	September 30, 2017		December 31, 2016
Accrued compensation and benefits	$	14,192	$	14,382
Accrued consulting and professional fees		7,183		9,488
Accrued research and development services		5,681		8,551
Accrued sales allowances		3,721		1,999
Other		2,404		1,609
	$	33,181	$	36,029

Investment Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Schedule of Investment Securities Classified as Available-for-Sale

Investment securities, all classified as available-for-sale, consisted of the following (in thousands):

	September 30, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	66,319	$	1	$	(13	)	$	66,307
Government sponsored enterprise securities		35,711		—		(5	)		35,706
Corporate debt securities		61,966		—		(38	)		61,928
Commercial paper		90,095		—		(27	)		90,068
	$	254,091	$	1	$	(83	)	$	254,009

	December 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	82,484	$	6	$	(3	)	$	82,487
Government sponsored enterprise securities		73,789		1		(5	)		73,785
Corporate debt securities		79,190		—		(72	)		79,118
Commercial paper		129,861		165		—			130,026
	$	365,324	$	172	$	(80	)	$	365,416

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements of Cash Equivalents and Available-For-Sale Investment Securities

			Fair Value Measurements at Reporting Date Using
	September 30, 2017		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	44,411	$	44,411	$	—	$	—
U.S. Treasury notes		66,307	$	66,307		—		—
Government sponsored enterprise securities		65,685		—		65,685		—
Corporate debt securities		78,942		—		78,942		—
Commercial paper		110,050		—		110,050		—
	$	365,395	$	110,718	$	254,677	$	—

			Fair Value Measurements at Reporting Date Using
	December 31, 2016		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	129,292	$	129,292	$	—	$	—
U.S. Treasury notes		82,487		82,487		—		—
Government sponsored enterprise securities		88,773		—		88,773		—
Corporate debt securities		82,857		—		82,857		—
Commercial paper		140,024		—		140,024		—
	$	523,433	$	211,779	$	311,654	$	—

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 30, 2016	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Accounts receivable written off			$ 0	$ 0
One-time contingent regulatory milestone payment pursuant to agreement with Ipsen Group	$ 8,000,000
Finite-lived intangible assets, net	$ 8,000,000
Amortization of intangible assets		$ 400,000	1,108,000	$ 615,000
Estimated future amortization expense, remainder of 2017		400,000	400,000
Estimated future amortization expense, 2018		1,500,000	1,500,000
Estimated future amortization expense, 2019		1,500,000	1,500,000
Estimated future amortization expense, 2020		1,500,000	1,500,000
Estimated future amortization expense, 2021		1,000,000	$ 1,000,000
Net revenue		$ 0

Net Loss Per Share - Additional Information (Detail) - shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Antidilutive securities to purchase common stock	20,154,000	14,463,000

Stock-Based Compensation - Summary of Stock-based Compensation Expense Included in Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 19,698	$ 14,009	$ 53,513	$ 39,847
Cost of product sales
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,210	308	2,971	497
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	6,877	4,319	18,598	13,495
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 11,611	$ 9,382	$ 31,944	$ 25,855

Balance Sheet Details - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw material	$ 4,088	$ 1,820
Finished goods	1,448	2,355
Inventory	$ 5,536	$ 4,175

Balance Sheet Details - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued compensation and benefits	$ 14,192	$ 14,382
Accrued consulting and professional fees	7,183	9,488
Accrued research and development services	5,681	8,551
Accrued sales allowances	3,721	1,999
Other	2,404	1,609
Accrued liabilities	$ 33,181	$ 36,029

Investment Securities - Schedule of Investment Securities Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 254,091	$ 365,324
Unrealized Gains	1	172
Unrealized Losses	(83)	(80)
Estimated Fair Value	254,009	365,416
U.S. Treasury notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66,319	82,484
Unrealized Gains	1	6
Unrealized Losses	(13)	(3)
Estimated Fair Value	66,307	82,487
Government sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,711	73,789
Unrealized Gains		1
Unrealized Losses	(5)	(5)
Estimated Fair Value	35,706	73,785
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,966	79,190
Unrealized Losses	(38)	(72)
Estimated Fair Value	61,928	79,118
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	90,095	129,861
Unrealized Gains		165
Unrealized Losses	(27)
Estimated Fair Value	$ 90,068	$ 130,026

Investment Securities - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Available-for-sale, investment securities held with maturity dates more than one year and less than two years	$ 10,900,000	$ 0

Fair Value Measurements - Fair Value Measurements of Cash Equivalents and Available-For-Sale Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	$ 365,395	$ 523,433
Money market fund
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	44,411	129,292
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	110,718	211,779
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Money market fund
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	44,411	129,292
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	254,677	311,654
U.S. Treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	66,307	82,487
U.S. Treasury notes \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	66,307	82,487
Government sponsored enterprise securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	65,685	88,773
Government sponsored enterprise securities \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	65,685	88,773
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	78,942	82,857
Corporate debt securities \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	78,942	82,857
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	110,050	140,024
Commercial paper \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	$ 110,050	$ 140,024

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References + Details

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		9 Months Ended
	Aug. 31, 2016	Jan. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Class Of Stock [Line Items]
Net proceeds from sale of common stock	$ 215,900,000	$ 281,600,000	$ 26,397,000	$ 515,506,000
Share of common stock issued	6,969,696	10,344,827
Common stock, par value			$ 0.0001		$ 0.0001
Value of shares purchased by Baker Entities in public offerings			$ 12,000		$ 12,000
Option To Purchase Additional Shares
Class Of Stock [Line Items]
Share of common stock issued	909,090
Registration Rights Agreement
Class Of Stock [Line Items]
Common stock, par value		$ 0.0001
Expiration period		10 years
Maximum amount of expense agreed to bear under the agreement		$ 50,000
Registration Rights Agreement \| Baker Brothers Life Sciences L.P.
Class Of Stock [Line Items]
Value of shares purchased by Baker Entities in public offerings	$ 43,000,000	$ 75,000,000

Commitments and Contingencies - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Other Commitments [Line Items]
Restricted cash	$ 2,475,000	$ 2,375,000
Corporate Credit Card Program \| Letter of Credit
Other Commitments [Line Items]
Restricted cash		$ 2,000,000
Maximum
Other Commitments [Line Items]
Percentage of royalty payments obligation on net product sales	2.00%

Recent Accounting Pronouncements - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2017 Source	Mar. 31, 2017 USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of source of revenue \| Source	1
ASU 2016-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Adoption of new accounting pronouncement deferred tax assets increased to record unrecognized excess tax benefits		$ 36.8
Increase to additional paid-in capital with increase to accumulated deficit		0.3
Deferred tax assets increase to record excess tax benefit		$ 0.1