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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Jul. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
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		125,006,723

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 74,182	$ 69,418
Investment securities, available-for-sale	182,673	271,924
Accounts receivable, net	25,696	17,343
Interest and other receivables	986	1,087
Inventory	4,737	5,248
Prepaid expenses	12,822	8,457
Total current assets	301,096	373,477
Property and equipment, net	2,760	2,662
Intangible assets, net	4,800	5,538
Restricted cash	3,111	2,475
Other assets	3,193	354
Total assets	314,960	384,506
Liabilities and stockholders’ equity
Accounts payable	3,333	8,786
Accrued liabilities	45,881	40,244
Total current liabilities	49,214	49,030
Long-term liabilities	1,026	191
Total liabilities	50,240	49,221
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at June 30, 2018 and December 31, 2017; no shares issued and outstanding at June 30, 2018 and December 31, 2017
Common stock, $0.0001 par value; 225,000,000 shares authorized at June 30, 2018 and December 31, 2017; 124,999,365 shares and 124,410,552 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	12	12
Additional paid-in capital	1,606,441	1,559,343
Accumulated deficit	(1,341,233)	(1,223,671)
Accumulated other comprehensive loss	(500)	(399)
Total stockholders’ equity	264,720	335,285
Total liabilities and stockholders’ equity	$ 314,960	$ 384,506

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
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	124,999,365	124,410,552
Common stock, shares outstanding	124,999,365	124,410,552

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Total revenues	$ 57,063	$ 30,475	$ 105,931	$ 45,761
Operating expenses
Type of Cost, Good or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Cost of product sales	$ 3,562	$ 2,224	$ 5,715	$ 4,487
License fees and royalties	1,516	982	2,848	1,657
Research and development	46,592	34,180	85,868	69,589
Selling, general and administrative	69,472	61,125	130,398	126,785
Total operating expenses	121,142	98,511	224,829	202,518
Loss from operations	(64,079)	(68,036)	(118,898)	(156,757)
Interest income, net	1,279	993	2,449	1,956
Other expense	(247)		(247)
Loss before income taxes	(63,047)	(67,043)	(116,696)	(154,801)
Income tax expense	219	398	866	483
Net loss	$ (63,266)	$ (67,441)	$ (117,562)	$ (155,284)
Net loss per common share, basic and diluted	$ (0.51)	$ (0.55)	$ (0.94)	$ (1.27)
Weighted average common shares outstanding, basic and diluted	124,910	122,122	124,819	121,888

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (63,266)	$ (67,441)	$ (117,562)	$ (155,284)
Other comprehensive gain (loss):
Unrealized gain (loss) on investment securities	195	(188)	(103)	(199)
Foreign currency translation adjustments	4	(3)	2	(4)
Comprehensive loss	$ (63,067)	$ (67,632)	$ (117,663)	$ (155,487)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net loss	$ (117,562)	$ (155,284)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	40,994	33,815
(Amortization of premiums) and accretion of discounts on investment securities, net	(241)	(297)
Amortization of intangible assets	738	738
Loss on strategic investments	247
Depreciation	734	577
Loss on disposal of assets	32
Changes in operating assets and liabilities:
Accounts receivable, net	(8,353)	(5,691)
Interest and other receivables	101	453
Inventory	782	(1,927)
Prepaid expenses	(4,365)	(498)
Other assets	64	263
Accounts payable	(5,523)	(324)
Accrued liabilities	5,406	1,253
Deferred revenue		(2,644)
Long-term liabilities	835	105
Net cash used in operating activities	(86,111)	(129,461)
Cash flows from investing activities
Purchases of investment securities	(85,762)	(250,007)
Maturities of investment securities	175,151	341,990
Purchases of strategic investments	(3,150)
Purchases of property and equipment	(563)	(749)
Net cash provided by investing activities	85,676	91,234
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	5,833	18,500
Net cash provided by financing activities	5,833	18,500
Effect of exchange rate changes on cash	2	(4)
Net increase (decrease) in cash, cash equivalents and restricted cash	5,400	(19,731)
Cash, cash equivalents and restricted cash
Beginning of period	71,893	165,995
End of period	77,293	146,264
Supplemental disclosure of noncash information:
Property and equipment purchases in accounts payable and accrued liabilities	301	43
Stock-based compensation capitalized in inventory	$ (271)	$ 99

Organization and Business	6 Months Ended
Organization and Business	Jun. 30, 2018
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. In April 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 in May 2016.

Basis of Presentation and Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

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, 2017 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.

Reclassifications

The Company has reclassified certain prior period amounts to conform to current period presentation. Specifically, it has reclassified income tax expense previously included within selling, general and administrative expense and presented it separately in the Condensed Consolidated Statement of Operations. This reclassification reduced the Company’s previously stated selling, general and administrative expense and total operating expense for the three and six months ended June 30, 2017 by $0.4 million and $0.5 million, respectively. The reclassification had no impact on the Company’s net loss or stockholders’ equity as previously reported.

In addition, pursuant to the adoption of ASU 2016-18, Statement of Cash Flows: Restricted Cash, the Company is presenting restricted cash with cash and cash equivalents in the beginning-of-period and end-of-period total amounts on its Condensed Consolidated Statements of Cash Flows. This reclassification reduced the Company’s previously stated net cash used in operations and net decrease in cash and cash equivalents for the six months ended June 30, 2017 by $0.1 million. The reclassification had no impact on the Company’s balance sheets as previously reported. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the consolidated balance sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in thousands).

	Six Months Ended June 30, 2018				Six Months Ended June 30, 2017
	Beginning of period		End of period		Beginning of period		End of period
Cash and cash equivalents	$	69,418	$	74,182	$	163,620	$	143,789
Restricted cash		2,475		3,111		2,375		2,475
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	71,893	$	77,293	$	165,995	$	146,264

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 June 30, 2018, 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 $0.7 million for each of the three and six months ended June 30, 2018 and 2017, respectively. As of June 30, 2018, estimated future amortization expense related to the Company’s intangible asset was $0.7 million for the remainder of 2018, $1.5 million for each of 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.

Strategic Investments

In May 2018, the Company signed an Exclusivity Deed (the “Deed”) with Neuren Pharmaceuticals Limited (“Neuren”) that provides for exclusive negotiations for a period of three months from the date of the Deed. Under the terms of the Deed, the Company invested $3.1 million to subscribe for 1,330,000 shares of the company and paid $0.9 million for the exclusivity right, which was recorded in selling, general and administrative expenses in the Condensed Consolidated Statement of Operations for the three and six months ended June 30, 2018. At June 30, 2018, the Company continues to hold the equity securities as a strategic investment in which the Company does not have a controlling interest or significant influence. Publicly held equity securities are measured using quoted prices in their respective active markets with changes recorded through net gains on strategic investments on the statement of operations. Net loss on strategic investments recognized in the Condensed Consolidated Statements of Operations in each of the three and six months ended June 30, 2018 was $0.2 million. As of June 30, 2018, the aggregate carrying amount of the Company’s strategic equity investment was $2.9 million included in other assets on the Condensed Consolidated Balance Sheet.

Revenue Recognition

Product Sales, Net

The Company’s net product sales consist of U.S. sales of NUPLAZID. Effective January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606), and all the related amendments to all of the contracts using the modified-retrospective method. While results for reporting periods beginning after January 1, 2018 are presented under the new guidance, prior period amounts are not adjusted and continue to be reported under the accounting standards in effect for the prior period. The accounting policy for revenue recognition for periods prior to January 1, 2018 is described in Note 2 of the Notes to the Consolidated Financial Statements included in the Company’s Annual Report. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity 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 entity satisfies a 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, 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. Payment terms differ by customer, but typically range from 31 to 35 days from the date of shipment. Revenue for the Company’s product sales has not been adjusted for the effects of a financing component as the Company expects, at contract inception, that the period between when the Company’s transfers control of the product and when the Company receives payment will be one year or less. No cumulative effect adjustment to the opening balance of retained earnings was necessary upon adoption, and there is no reconciliation of the Company’s condensed consolidated statement of operations, as no revenue recognition differences were identified when comparing the revenue recognition criteria under Topic 606 to previous requirements.

NUPLAZID was approved by the FDA in April 2016 and the Company commenced shipments of NUPLAZID to specialty pharmacies (“SPs”) and specialty distributors (“SDs”) in late May 2016. Prior to the second quarter of 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.

The effect on income from operations and on net income is that the Company is able to recognize revenue earlier using 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 the second quarter of 2017.

Product shipping and handling costs are included in cost of product sales.

The Company recognizes revenue from product sales at the net sales price (the “transaction price”) which includes estimates of variable consideration for which reserves are established and reflects each of these as either a reduction to the related account receivable or as an accrued liability, depending on how the allowance is settled. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company 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 estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment.

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.

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.

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 for product returns, 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	6 Months Ended
Net Loss Per Share	Jun. 30, 2018
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 June 30, 2018 and 2017, stock options, employee stock purchase plan rights, and warrants totaling approximately 19,834,000 shares and 16,563,000 shares, respectively, were excluded from the calculation of diluted net loss per share as their effect would have been anti-dilutive.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2018

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 June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Cost of product sales	$	1,137	$	881	$	2,187	$	1,761
Research and development		7,894		6,420		15,551		11,721
Selling, general and administrative		11,521		10,943		23,256		20,333
	$	20,552	$	18,244	$	40,994	$	33,815

Balance Sheet Details

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Details

5. Balance Sheet Details

Inventory consisted of the following (in thousands):

	June 30, 2018		December 31, 2017
Raw material	$	3,334	$	4,084
Work in process		744		—
Finished goods		659		1,164
	$	4,737	$	5,248

Accrued liabilities consisted of the following (in thousands):

	June 30, 2018		December 31, 2017
Accrued consulting and professional fees	$	16,086	$	9,395
Accrued compensation and benefits		11,805		15,260
Accrued research and development services		8,900		9,487
Accrued sales allowances		5,853		3,591
Other		3,237		2,511
	$	45,881	$	40,244

Investments

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Investments

6. Investments

The carrying value and amortized cost of the Company’s investments, summarized by major security type, consisted of the following (in thousands):

	June 30, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	—	$	—	$	—		$	—
Government sponsored enterprise securities		—		—		—			—
Corporate debt securities		139,304		—		(502	)		138,802
Commercial paper		43,879		6		(14	)		43,871
Equity securities		3,149		—		(247	)		2,902
	$	186,332	$	6	$	(763	)	$	185,575

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	32,976	$	—	$	(12	)	$	32,964
Government sponsored enterprise securities		10,082		—		(10	)		10,072
Corporate debt securities		138,650		1		(321	)		138,330
Commercial paper		90,623		—		(65	)		90,558
	$	272,331	$	1	$	(408	)	$	271,924

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 June 30, 2018 and December 31, 2017, the Company held $44.2 million and $48.7 million, respectively, of available-for-sale investment securities with contractual maturity dates of more than one year and less than two years. The Company has classified all equity securities as other assets on its consolidated balance sheets.

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 June 30, 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
June 30, 2018:
U.S. Treasury notes	$	—	$	—		$	—	$	—	$	—	$	—
Government sponsored enterprise securities		—		—			—		—		—		—
Corporate debt securities		136,308		(502	)		—		—		136,308		(502	)
Commercial paper		24,061		(14	)		—		—		24,061		(14	)
Total	$	160,369	$	(516	)	$	—	$	—	$	160,369	$	(516	)
December 31, 2017:
U.S. Treasury notes	$	32,964	$	(12	)	$	—	$	—		32,964		(12	)
Government sponsored enterprise securities		10,072		(10	)		—		—		10,072		(10	)
Corporate debt securities		129,820		(321	)		—		—		129,820		(321	)
Commercial paper		90,558		(65	)		—		—		90,558		(65	)
Total	$	263,414	$	(408	)	$	—	$	—	$	263,414	$	(408	)

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 June 30, 2018 and December 31, 2017.

Fair Value Measurements

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

7. Fair Value Measurements

The Company’s investments include cash equivalents, 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 and equity investments. 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, available-for-sale investment securities and equity securities are classified within the fair value hierarchy as defined by authoritative guidance. The Company’s investment securities and equity 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 June 30, 2018 and December 31, 2017.

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, available-for-sale investment securities and equity securities at June 30, 2018 and December 31, 2017 consisted of the following (in thousands):

			Fair Value Measurements at Reporting Date Using
	June 30, 2018		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	18,132	$	18,132	$	—	$	—
U.S. Treasury notes		—		—		—		—
Equity securities		2,902		2,902		—		—
Government sponsored enterprise securities		—		—		—		—
Corporate debt securities		145,463		—		145,463		—
Commercial paper		89,284		—		89,284		—
	$	255,781	$	21,034	$	234,747	$	—

			Fair Value Measurements at Reporting Date Using
	December 31, 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	$	38,057	$	38,057	$	—	$	—
U.S. Treasury notes		32,964		32,964		—		—
Government sponsored enterprise securities		10,072		—		10,072		—
Corporate debt securities		154,396		—		154,396		—
Commercial paper		98,052		—		98,052		—
	$	333,541	$	71,021	$	262,520	$	—

- 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	6 Months Ended
Stockholders' Equity	Jun. 30, 2018
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. Private Equity Financings In December 2012, the Company raised net proceeds of $80.5 million through the sale of 19,000,000 shares of its common stock at a price of $4.43 per share and the sale of warrants to purchase 500,000 shares of its common stock at a price of $4.42 per warrant share in a private equity financing. The warrants have an exercise price of $0.01 per share and will expire on December 17, 2019. In accordance with authoritative accounting guidance, the warrants’ value of $2.2 million was determined on the date of grant using the Black-Scholes model with the following assumptions: risk free interest rate of 1.1 percent, volatility of 105.8 percent, a 7.0 year term and no dividend yield. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the warrants to purchase 500,000 shares of common stock, all of which remained outstanding at June 30, 2018, may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent following such exercise.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

9. Commitments and Contingencies

Leases and Other Long-Term Commitments

In May 2018, the Company entered into a lease agreement to lease facilities under a noncancelable operating lease that expires January 2026.

Estimated annual future minimum payments related to the Company’s operating leases were as follows at June 30, 2018 (in thousands):

2018	$	1,375
2019		1,880
2020		1,192
2021		886
2022		898
Thereafter		2,848
	$	9,079

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 for $2.0 million, which has automatic annual extensions and is fully secured by restricted cash.

Fleet Program

In connection with the Company’s fleet program, the Company established letters of credit with the leasing entities totaling $0.7 million, which have automatic annual extensions and are fully secured by restricted cash.

Legal Proceedings

Between July 19 and July 23, 2018, in the wake of recent negative publicity about NUPLAZID, two purported Company stockholders filed putative securities class action complaints (captioned Staublein v. ACADIA Pharmaceuticals, Inc., Case No. 18-cv-01647-JAH-MDD, and Stone v. ACADIA Pharmaceuticals Inc., Case No. 18-cv-01672-LAB-JMA) in the U.S. District Court for the Southern District of California against the Company and certain of its current executive officers. The complaints generally allege that defendants violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 by making materially false and misleading statements regarding the Company’s business, operations, and prospects by failing to disclose that adverse events and safety concerns regarding NUPLAZID threatened initial and continuing FDA approval, and by failing to disclose that the Company engaged in business practices likely to attract regulatory scrutiny. The complaints seek unspecified monetary damages and other relief. The Company has assessed such legal proceedings, and given the unpredictability inherent in litigation, the Company cannot predict the outcome of these matters. At this time, the Company is unable to estimate possible losses or ranges of losses that may result from such legal proceedings, and it has not accrued any amounts in connection with such legal proceedings other than ongoing attorneys’ fees.

Recent Accounting Pronouncements	6 Months Ended
Recent Accounting Pronouncements	Jun. 30, 2018
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Recent Accounting Pronouncements	10. Recent Accounting Pronouncements In December 2017, the U.S. Securities and Exchange Commission (“SEC”) staff issued SAB 118, which provides guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the “Act”). SAB 118 was issued to address the application of US GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. In accordance with SAB 118, the Company has provisionally determined that there is no deferred tax benefit or expense with respect to the remeasurement of certain deferred tax assets and liabilities due to the full valuation allowance against net deferred tax assets. The Company is still analyzing certain aspects of the Act and refining its calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts. Additional analysis of the law and the impact to the Company will be performed and any impact will be recorded in the respective quarter in 2018. 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 was effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company adopted this guidance in the first quarter of 2018, using a retrospective transition method. The adoption of this ASU impacted the presentation of cash flows, with inclusion of restricted cash flows for each of the presented periods. 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 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. In January 2018, the FASB issued ASU 2018-01, Leases: Land Easement Practical Expedient for Transition to Topic 842, which facilitates the implementation of ASU 2016-02. ASU 2018-01 would give entities the option to apply ASU 2016-02 as of the effective date, rather than as of the beginning of the earliest period presented. Under this additional option transition method, a cumulative-effect adjustment would be recognized in the opening balance of retained earnings in the period of adoption. The effective date of the transition requirements for the amendment is the same as the effective date and transition requirements in ASU 2016-02. While the Company is currently evaluating its significant lease arrangements to assess the potential 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 (Topic 606), which supersedes nearly all existing revenue recognition guidance under GAAP. On January 1, 2018, the Company adopted ASU 2014-09 and all the related guidance.

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events On August 6, 2018 the Company entered into a license agreement with Neuren and obtained exclusive North American rights to develop and commercialize trofinetide for Rett syndrome and other indications. Under the terms of the agreement, Neuren will receive an upfront payment of $10.0 million and is eligible to receive milestone payments of up to $455.0 million, based on the achievement of certain development and annual net sales milestones. In addition, Neuren is eligible to receive tiered, escalating, double-digit percentage royalties based on net sales.

Basis of Presentation and Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

Reclassifications

	Six Months Ended June 30, 2018				Six Months Ended June 30, 2017
	Beginning of period		End of period		Beginning of period		End of period
Cash and cash equivalents	$	69,418	$	74,182	$	163,620	$	143,789
Restricted cash		2,475		3,111		2,375		2,475
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	71,893	$	77,293	$	165,995	$	146,264

Accounts Receivable

License Fees and Royalties

Strategic Investments

Revenue Recognition

Product Sales, Net

Product shipping and handling costs are included in cost of product sales.

- Definition

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.

+ References + Details

- 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

Basis of Presentation and Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the consolidated balance sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in thousands).

	Six Months Ended June 30, 2018				Six Months Ended June 30, 2017
	Beginning of period		End of period		Beginning of period		End of period
Cash and cash equivalents	$	69,418	$	74,182	$	163,620	$	143,789
Restricted cash		2,475		3,111		2,375		2,475
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	71,893	$	77,293	$	165,995	$	146,264

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

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 June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Cost of product sales	$	1,137	$	881	$	2,187	$	1,761
Research and development		7,894		6,420		15,551		11,721
Selling, general and administrative		11,521		10,943		23,256		20,333
	$	20,552	$	18,244	$	40,994	$	33,815

Balance Sheet Details (Tables)

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Inventory

Inventory consisted of the following (in thousands):

	June 30, 2018		December 31, 2017
Raw material	$	3,334	$	4,084
Work in process		744		—
Finished goods		659		1,164
	$	4,737	$	5,248

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	June 30, 2018		December 31, 2017
Accrued consulting and professional fees	$	16,086	$	9,395
Accrued compensation and benefits		11,805		15,260
Accrued research and development services		8,900		9,487
Accrued sales allowances		5,853		3,591
Other		3,237		2,511
	$	45,881	$	40,244

Investments (Tables)

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Carrying Value and Amortized Cost of Company’s Investments Summarized by Major Security Type

The carrying value and amortized cost of the Company’s investments, summarized by major security type, consisted of the following (in thousands):

	June 30, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	—	$	—	$	—		$	—
Government sponsored enterprise securities		—		—		—			—
Corporate debt securities		139,304		—		(502	)		138,802
Commercial paper		43,879		6		(14	)		43,871
Equity securities		3,149		—		(247	)		2,902
	$	186,332	$	6	$	(763	)	$	185,575

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	32,976	$	—	$	(12	)	$	32,964
Government sponsored enterprise securities		10,082		—		(10	)		10,072
Corporate debt securities		138,650		1		(321	)		138,330
Commercial paper		90,623		—		(65	)		90,558
	$	272,331	$	1	$	(408	)	$	271,924

Summary of Gross Unrealized Losses and Fair Value of 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
June 30, 2018:
U.S. Treasury notes	$	—	$	—		$	—	$	—	$	—	$	—
Government sponsored enterprise securities		—		—			—		—		—		—
Corporate debt securities		136,308		(502	)		—		—		136,308		(502	)
Commercial paper		24,061		(14	)		—		—		24,061		(14	)
Total	$	160,369	$	(516	)	$	—	$	—	$	160,369	$	(516	)
December 31, 2017:
U.S. Treasury notes	$	32,964	$	(12	)	$	—	$	—		32,964		(12	)
Government sponsored enterprise securities		10,072		(10	)		—		—		10,072		(10	)
Corporate debt securities		129,820		(321	)		—		—		129,820		(321	)
Commercial paper		90,558		(65	)		—		—		90,558		(65	)
Total	$	263,414	$	(408	)	$	—	$	—	$	263,414	$	(408	)

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

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

			Fair Value Measurements at Reporting Date Using
	June 30, 2018		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	18,132	$	18,132	$	—	$	—
U.S. Treasury notes		—		—		—		—
Equity securities		2,902		2,902		—		—
Government sponsored enterprise securities		—		—		—		—
Corporate debt securities		145,463		—		145,463		—
Commercial paper		89,284		—		89,284		—
	$	255,781	$	21,034	$	234,747	$	—

			Fair Value Measurements at Reporting Date Using
	December 31, 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	$	38,057	$	38,057	$	—	$	—
U.S. Treasury notes		32,964		32,964		—		—
Government sponsored enterprise securities		10,072		—		10,072		—
Corporate debt securities		154,396		—		154,396		—
Commercial paper		98,052		—		98,052		—
	$	333,541	$	71,021	$	262,520	$	—

Commitments and Contingencies (Tables)

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Estimated Annual Future Minimum Payments under Operating Leases

Estimated annual future minimum payments related to the Company’s operating leases were as follows at June 30, 2018 (in thousands):

2018	$	1,375
2019		1,880
2020		1,192
2021		886
2022		898
Thereafter		2,848
	$	9,079

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	May 31, 2018	Apr. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Basis Of Presentation And Significant Accounting Policies [Line Items]
Net cash used in operations					$ (86,111,000)	$ (129,461,000)
Net decrease in cash and cash equivalents					5,400,000	(19,731,000)
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	$ 400,000	738,000	738,000
Estimated future amortization expense, remainder of 2018			700,000		700,000
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
Aggregate carrying amount of strategic equity investment			2,900,000		2,900,000
Loss on strategic investments			(200,000)		(247,000)
Revenue recognition			(1,341,233,000)		(1,341,233,000)			$ (1,223,671,000)
Exclusivity Deed \| Neuren
Basis Of Presentation And Significant Accounting Policies [Line Items]
Aggregate carrying amount of strategic equity investment	$ 3,100,000
Shares subscribed	1,330,000
ASU 2016-18
Basis Of Presentation And Significant Accounting Policies [Line Items]
Net cash used in operations						100,000
Net decrease in cash and cash equivalents						100,000
Topic 606 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cumulative-effect adjustment to retained earnings							$ 0
Topic 606 [Member] \| Difference effect of change - higher (lower)
Basis Of Presentation And Significant Accounting Policies [Line Items]
Revenue recognition			$ 0		$ 0
Selling, general and administrative expense
Basis Of Presentation And Significant Accounting Policies [Line Items]
Prior period reclassification adjustment				400,000		500,000
Selling, general and administrative expense \| Exclusivity Deed \| Neuren
Basis Of Presentation And Significant Accounting Policies [Line Items]
Payments for exclusivity right	$ 900,000
Total operating expense
Basis Of Presentation And Significant Accounting Policies [Line Items]
Prior period reclassification adjustment				$ 400,000		$ 500,000

Basis of Presentation and Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations [Abstract]
Cash and cash equivalents	$ 74,182	$ 69,418	$ 143,789	$ 163,620
Restricted cash	3,111	2,475	2,475	2,375
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 77,293	$ 71,893	$ 146,264	$ 165,995

Net Loss Per Share - Additional Information (Detail) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Antidilutive securities to purchase common stock	19,834,000	16,563,000

Stock-Based Compensation - Summary of Stock-based Compensation Expense Included in Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 20,552	$ 18,244	$ 40,994	$ 33,815
Cost of product sales
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,137	881	2,187	1,761
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	7,894	6,420	15,551	11,721
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 11,521	$ 10,943	$ 23,256	$ 20,333

Balance Sheet Details - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw material	$ 3,334	$ 4,084
Work in process	744
Finished goods	659	1,164
Inventory	$ 4,737	$ 5,248

Balance Sheet Details - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued consulting and professional fees	$ 16,086	$ 9,395
Accrued compensation and benefits	11,805	15,260
Accrued research and development services	8,900	9,487
Accrued sales allowances	5,853	3,591
Other	3,237	2,511
Accrued liabilities	$ 45,881	$ 40,244

Investments - Carrying Value and Amortized Cost of Company's Investments Summarized by Major Security Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Estimated Fair Value	$ 182,673	$ 271,924
Equity securities, Amortized Cost	3,149
Equity securities, Unrealized Losses	(247)
Equity securities, Estimated Fair Value	2,902
Debt and equity securities, Amortized Cost	186,332	272,331
Debt and equity securities, Unrealized Gains	6	1
Debt and equity securities, Unrealized Losses	(763)	(408)
Debt and equity securities, Estimated Fair Value	185,575	271,924
U.S. Treasury notes
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized Cost		32,976
Debt securities, Unrealized Losses		(12)
Debt securities, Estimated Fair Value		32,964
Government sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized Cost		10,082
Debt securities, Unrealized Losses		(10)
Debt securities, Estimated Fair Value		10,072
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized Cost	139,304	138,650
Debt securities, Unrealized Gains		1
Debt securities, Unrealized Losses	(502)	(321)
Debt securities, Estimated Fair Value	138,802	138,330
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized Cost	43,879	90,623
Debt securities, Unrealized Gains	6
Debt securities, Unrealized Losses	(14)	(65)
Debt securities, Estimated Fair Value	$ 43,871	$ 90,558

Investments - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Available-for-sale, investment securities held with maturity dates more than one year and less than two years	$ 44.2	$ 48.7

Investments - Summary of Gross Unrealized Losses and Fair Value of Available-For-Sale Investments in Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	$ 160,369	$ 263,414
Less Than 12 Months, Unrealized Losses	(516)	(408)
Total, Estimated Fair Value	160,369	263,414
Total, Unrealized Losses	(516)	(408)
U.S. Treasury notes
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value		32,964
Less Than 12 Months, Unrealized Losses		(12)
Total, Estimated Fair Value		32,964
Total, Unrealized Losses		(12)
Government sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value		10,072
Less Than 12 Months, Unrealized Losses		(10)
Total, Estimated Fair Value		10,072
Total, Unrealized Losses		(10)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	136,308	129,820
Less Than 12 Months, Unrealized Losses	(502)	(321)
Total, Estimated Fair Value	136,308	129,820
Total, Unrealized Losses	(502)	(321)
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	24,061	90,558
Less Than 12 Months, Unrealized Losses	(14)	(65)
Total, Estimated Fair Value	24,061	90,558
Total, Unrealized Losses	$ (14)	$ (65)

Fair Value Measurements - Fair Value Measurements of Cash Equivalents Available-For-Sale Investment Securities and Equity Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	$ 255,781	$ 333,541
Money market fund
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	18,132	38,057
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	21,034	71,021
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	18,132	38,057
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	234,747	262,520
U.S. Treasury notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure		32,964
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		32,964
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	2,902
Equity securities \| 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	2,902
Government sponsored enterprise securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure		10,072
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		10,072
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	145,463	154,396
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	145,463	154,396
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	89,284	98,052
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	$ 89,284	$ 98,052

Stockholders' Equity - Additional Information (Detail)	1 Months Ended			6 Months Ended
Stockholders' Equity - Additional Information (Detail)	Aug. 31, 2016 USD ($) shares	Jan. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2012 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) $ / shares
Class of Stock [Line Items]
Net proceeds from sale of common stock	$ 215,900,000	$ 281,600,000		$ 5,833,000	$ 18,500,000
Share of common stock issued \| shares	6,969,696	10,344,827	19,000,000
Common stock, par value \| $ / shares				$ 0.0001		$ 0.0001
Value of shares purchased by Baker Entities in public offerings				$ 12,000		$ 12,000
Proceed from sale of stock and warrants			$ 80,500,000
Common stock sale price per share \| $ / shares			$ 4.43
Expire on December 17, 2019
Class of Stock [Line Items]
Warrants issued \| shares			500,000
Warrants issuance price per share \| $ / shares			$ 4.42
Warrant exercise price \| $ / shares			$ 0.01
Warrant expiration date				Dec. 17, 2019
Issuance of warrant value			$ 2,200,000
Warrants outstanding \| shares			500,000
Description of warrant				Per their terms, the warrants to purchase 500,000 shares of common stock, all of which remained outstanding at June 30, 2018, may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent following such exercise.
Expire on December 17, 2019 \| Risk Free Interest Rate
Class of Stock [Line Items]
Warrants outstanding, measurement input			1.1
Expire on December 17, 2019 \| Volatility Percentage
Class of Stock [Line Items]
Warrants outstanding, measurement input			105.8
Expire on December 17, 2019 \| Warrant Term
Class of Stock [Line Items]
Warrant term			7 years
Expire on December 17, 2019 \| Dividend Yield
Class of Stock [Line Items]
Warrants outstanding, measurement input			0
Registration Rights Agreement
Class of Stock [Line Items]
Common stock, par value \| $ / shares		$ 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
Option To Purchase Additional Shares
Class of Stock [Line Items]
Share of common stock issued \| shares	909,090

Commitments and Contingencies - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Other Commitments [Line Items]
Operating lease, expiration year	2026-01
Restricted cash	$ 3,111,000	$ 2,475,000	$ 2,475,000	$ 2,375,000
Letter of Credit [Member] \| Corporate Credit Card Program
Other Commitments [Line Items]
Restricted cash	2,000,000
Letter of Credit [Member] \| Fleet Program
Other Commitments [Line Items]
Restricted cash	$ 700,000
Maximum
Other Commitments [Line Items]
Percentage of royalty payments obligation on net product sales	2.00%

Commitments and Contingencies - Estimated Annual Future Minimum Payments under Operating Leases (Detail) $ in Thousands	Jun. 30, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 1,375
2019	1,880
2020	1,192
2021	886
2022	898
Thereafter	2,848
Operating Leases, Future Minimum Payments Due, Total	$ 9,079

Recent Accounting Pronouncements - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($)
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Deferred tax benefit or expense related to remeasurement of deferred tax assets and liabilities	$ 0

Subsequent Events - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Aug. 06, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Subsequent Event [Line Items]
Upfront payment		$ 3,562,000	$ 2,224,000	$ 5,715,000	$ 4,487,000
Subsequent Event \| License \| Neuren \| North America
Subsequent Event [Line Items]
Upfront payment	$ 10,000,000
Subsequent Event \| License \| Neuren \| Maximum \| North America
Subsequent Event [Line Items]
Milestone payments payable	$ 455,000,000