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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Jul. 29, 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	CYTK
Entity Registrant Name	CYTOKINETICS INC
Entity Central Index Key	0001061983
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		54,627,997

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 46,955	$ 125,206
Short-term investments	184,986	143,685
Accounts receivable	236	1,112
Contract assets	10,375	0
Prepaid and other current assets	1,677	4,292
Total current assets	244,229	274,295
Long-term investments	0	16,518
Property and equipment, net	2,598	3,568
Other assets	412	429
Total assets	247,239	294,810
Current liabilities:
Accounts payable	1,336	5,253
Accrued liabilities	16,090	17,392
Contract liabilities	8,132	0
Deferred revenue, current	0	9,572
Current portion of long-term debt	1,703	0
Other current liabilities	28	227
Total current liabilities	27,289	32,444
Long-term debt, net	30,662	31,777
Liability related to the sale of future royalties, net	113,144	104,650
Deferred revenue, non-current	0	15,000
Other long-term liabilities	974	1,097
Total liabilities	172,069	184,968
Commitments and contingencies	0	0
Stockholders’ equity:
Preferred stock, $0.001 par value	0	0
Common stock, $0.001 par value	55	54
Additional paid-in capital	762,887	755,526
Accumulated other comprehensive income	450	343
Accumulated deficit	(688,222)	(646,081)
Total stockholders’ equity	75,170	109,842
Total liabilities and stockholders’ equity	$ 247,239	$ 294,810

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Common stock, par value	$ 0.001	$ 0.001

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - 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:
Research and development, milestone, grant and other revenues, net	$ 4,680	$ (1,889)	$ 8,265	$ 818
Total revenues	6,215	3,053	11,483	7,206
Operating expenses:
Research and development	21,582	19,809	43,717	39,098
General and administrative	8,046	8,438	17,310	16,553
Total operating expenses	29,628	28,247	61,027	55,651
Operating loss	(23,413)	(25,194)	(49,544)	(48,445)
Interest expense	(898)	(782)	(1,761)	(1,540)
Non-cash interest expense on liability related to sale of future royalties	(4,338)	(3,717)	(8,467)	(6,012)
Interest and other income, net	1,126	612	1,968	1,049
Net loss	$ (27,523)	$ (29,081)	$ (57,804)	$ (54,948)
Net loss per share - basic and diluted	$ (0.51)	$ (0.60)	$ (1.07)	$ (1.22)
Weighted-average shares in net loss per share — basic and diluted	54,293	48,218	54,178	44,910
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	$ (39)	$ (78)	$ 107	$ (223)
Comprehensive loss	(27,562)	(29,159)	(57,697)	(55,171)
License Revenues [Member]
Revenues:
License revenues	$ 1,535	$ 4,942	$ 3,218	$ 6,388

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net loss	$ (57,804)	$ (54,948)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense on liability related to sale of future royalties	8,467	6,036
Non-cash equity-related expense	4,908	4,141
Depreciation of property and equipment	1,291	860
Interest receivable and amortization on investments	(500)	0
(Gain) loss on disposal of equipment	0	(82)
Non-cash interest expense related to long-term debt	588	278
Changes in operating assets and liabilities:
Accounts receivable	876	24
Contract assets	9,038	0
Prepaid and other assets	2,188	(2,663)
Accounts payable	(3,918)	(1,888)
Accrued and other liabilities	(1,597)	(3,912)
Contract liabilities	(10,618)	0
Deferred revenue	(9,572)	(51)
Net cash used in operating activities	(56,653)	(52,205)
Cash flows from investing activities:
Purchases of investments	(132,208)	(201,531)
Sales and maturities of investments	108,477	66,928
Purchases of property and equipment	(321)	(1,646)
Net cash used in investing activities	(24,052)	(136,249)
Cash flows from financing activities:
Public offerings of common stock, net of issuance costs	0	112,232
Sale of future royalties, net of issuance costs	0	90,621
Issuance of common stock related to sale of future royalties, net of issuance costs	0	7,560
Issuance of equity for stock-based awards and warrants, net	2,454	11,878
Net cash provided by financing activities	2,454	222,291
Net increase (decrease) in cash and cash equivalents	(78,251)	33,837
Cash and cash equivalents, beginning of period	125,206	66,874
Cash and cash equivalents, end of period	$ 46,955	$ 100,711

Organization and Significant Accounting Policies	6 Months Ended
Organization and Significant Accounting Policies	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Significant Accounting Policies	Note 1 — Organization and Significant Accounting Policies Cytokinetics, Incorporated (the “Company”, “we” or “our”) was incorporated under the laws of the state of Delaware on August 5, 1997. The Company is a late stage biopharmaceutical company focused on the discovery and development of novel small molecule therapeutics that modulate muscle function for the potential treatment of serious diseases and medical conditions. Our financial statements contemplate the conduct of our operations in the normal course of business. We have incurred an accumulated deficit of $688.2 million since inception and there can be no assurance that we will attain profitability. The Company anticipates that it will have operating losses and net cash outflows in future periods. We are subject to risks common to late stage biopharmaceutical companies including, but not limited to, development of new drug candidates, dependence on key personnel, and the ability to obtain additional capital as needed to fund our future plans. Our liquidity will be impaired if sufficient additional capital is not available on terms acceptable to us. To date, we have funded operations primarily through sales of our common stock, contract payments under our collaboration agreements, sale of future royalties, debt financing arrangements, sales of our convertible preferred stock, government grants and interest income. Until we achieve profitable operations, we intend to continue to fund operations through payments from strategic collaborations, additional sales of equity securities, grants and debt financings. We have never generated revenues from commercial sales of our drugs and may not have drugs to market for at least several years, if ever. Our success is dependent on our ability to enter into new strategic collaborations and/or raise additional capital and to successfully develop and market one or more of our drug candidates. As a result, we may choose to raise additional capital through equity or debt financings to continue to fund operations in the future. We cannot be certain that sufficient funds will be available from such a financing or through a collaborator when required or on satisfactory terms. Additionally, there can be no assurance that our drug candidates will be accepted in the marketplace or that any future products can be developed or manufactured at an acceptable cost. These factors could have a material adverse effect on our future financial results, financial position and cash flows. Based on the current status of our research and development activities, we believe that our existing cash, cash equivalents and investments will be sufficient to fund cash requirements for at least the next 12 months from the filing date of this Quarterly Report on Form 10-Q. If, at any time, our prospects for financing research and development programs decline, we may decide to reduce research and development expenses by delaying, discontinuing or reducing funding of one or more of our research or development programs. Alternatively, we might raise funds through strategic collaborations, public or private financings or other arrangements. Such funding, if needed, may not be available on favorable terms, or at all. These financial statements do not include any adjustments that might result from the outcome of this uncertainty. Basis of Presentation Our condensed consolidated financial statements include the accounts of Cytokinetics and our wholly-owned subsidiary. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. The financial statements include all adjustments (consisting only of normal recurring adjustments) that management believes are necessary for the fair statement of our financial information. These interim results are not necessarily indicative of results to be expected for the full fiscal year or any future interim period. The balance sheet at December 31, 2017 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. The financial statements and related disclosures have been prepared with the presumption that users of the interim financial statements have read or have access to the audited financial statements for the preceding fiscal year. Accordingly, these financial statements should be read in conjunction with the audited financial statements and notes thereto contained in the Company’s Form 10-K for the year ended December 31, 2017, as filed with the SEC. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the condensed consolidated financial statements and reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, investments, accrued research and development expenses, other long-lived assets, stock-based compensation and the valuation of deferred tax assets. We base our estimates on our historical experience and also on assumptions that we believe are reasonable; however, actual results could significantly differ from those estimates. Revenue Recognition – Adoption of Revenue from Contracts with Customers ASC 606 On January 1, 2018, we adopted Revenue from Contracts with Customers (ASC 606), using the modified retrospective method. On January 1, 2018, for contracts within the scope of ASC 606, we recognized a contract asset or liability and reduced our accumulated deficit by $15.7 million for the effect of adopting ASC 606 and did not revise our prior period financial statements. Pursuant to ASC 606, to recognize revenue from a contract with a customer, we: (i) identify our contracts with our customers; (ii) identify our distinct performance obligations in each contract; (iii) determine the transaction price of each contract; (iv) allocate the transaction price to the performance obligations; and (v) recognize revenue as we satisfy our performance obligations. At contract inception, we assess the goods or services promised within each contract and assess whether each promised good or service is distinct and determine those that are performance obligations. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaborative Arrangements We enter into collaborative arrangements with partners that typically include payment to us for one of more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; and (iii) royalties on net sales of licensed products. Each of these payments results in collaboration or other revenues. Where a portion of non-refundable up-front fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. As part of the accounting for these arrangements, we must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation. The stand-alone selling price may include such items as, forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, to determine the transaction price to allocate to each performance obligation. For our collaboration agreements that include more than one performance obligation, such as a license combined with a commitment to perform research and development services, we make judgments to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. We evaluate our progress each reporting period and, if necessary, adjust the measure of a performance obligation and related revenue recognition. License Fees: If a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front license fees. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments: We use judgement to determine whether a milestone is considered probable of being reached. Using the most likely amount method, we include the value of a milestone payment in the consideration for a contract at inception if we then conclude achieving the milestone is more likely than not. Otherwise, we exclude the value of a milestone payment from contract consideration at inception and recognize revenue for a milestone at a later date, when we judge that it is more likely than not that the milestone will be achieved. If we conclude it is probable that a significant revenue reversal would not occur, the associated milestone is included in the transaction price. We then allocate the transaction price to each performance obligation on a relative stand-alone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, we re-evaluate the probability of achievement of such milestones and any related constraint, and if necessary, adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration and other revenues and earnings in the period of adjustment. Royalties: For contracts that include sales-based royalties, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied. To date, we have not recognized any royalty revenues resulting from contracts. Income Taxes We account for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. We establish valuation allowances when necessary to reduce deferred tax assets to the amounts expected to be realized. We recognize uncertain tax positions taken or expected to be taken on a tax return. Tax positions are initially recognized when it is more likely than not that the position will be sustained upon examination by the tax authorities. We measure our tax positions as the largest amount of tax benefit that is more likely than not of being realized upon ultimate settlement with the tax authority assuming full knowledge of the position and relevant facts. We recognize interest accrued related to unrecognized tax benefits and penalties as income tax expense. In December 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017. Staff Accounting Bulletin No. 118 ("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. We continue to analyze certain provisions of the Act including the application of new executive compensation limitation provisions under Internal Revenue Section 162(m). These items are subject to revisions from further analysis of the Tax Act and interpretation of any additional guidance issued by the U.S. Treasury Department, IRS, FASB, and other standard-setting and regulatory bodies. We did not record a provision for income tax for three and six months ended June 30, 2018 because we expect to report a net tax loss for the year ending December 31, 2018. Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, ‘Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments. ASU 2016-13 changes the impairment model for most financial assets and certain other instruments and is effective for annual and interim reporting periods beginning after December 15, 2019. We do not expect the adoption of ASU 2016-13 to have a material impact on our financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 requires us to record right-of-use asset and lease liability on the statement of financial position for operating leases with lease terms of more than 12 months and is effective for annual and interim reporting periods beginning on or after December 15, 2018. We expect to adopt this standard beginning in 2019 using the modified retrospective approach. We do not expect that this standard will have a material impact on our results of operations, but we do expect that upon adoption, it will have a material impact on our assets and liabilities. The primary effect of adoption will be the requirement to record right-of-use assets and corresponding lease obligations for current operating leases with lease terms of more than 12 months.

Net Loss Per Share

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

Note 2 — Net Loss Per Share

We excluded the following from diluted net loss per share because inclusion would have been antidilutive (in thousands):

	Six Months Ended
	June 30, 2018		June 30, 2017
Options to purchase common stock		5,421		6,170
Warrants to purchase common stock		100		310
Restricted Stock and Performance units		581		461
Shares issuable related to the ESPP		28		18
		6,130		6,959

Revenue Recognition

6 Months Ended

Jun. 30, 2018

Revenue Recognition [Abstract]

Revenue Recognition

Note 3 — Revenue Recognition

The performance obligations for our contract assets and liabilities relate to the research and development services for particular clinical programs, all of which we expect to complete in 2018.

We believe recognizing revenue as research and development services are performed provides a faithful depiction of the transfer of the services because completion of clinical programs results in data useful to determine satisfaction of our promise. We may fund research and development in advance of the performance of the services. When we complete our performance obligation, if we have received more than we incurred, we are obligated to return unused advance funding. We recognize these advance payments as deferred revenue until we perform the related services.

Our revenue for the three and six months ended June 30, 2018 was affected by adopting ASC 606 as follows (in thousands):

	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Research and development revenue using guidance in effect prior to ASC 606	$	70		$	(1,334	)
Impact of adoption of ASC 606		4,610			9,599
Research and development revenue	$	4,680		$	8,265

License revenue using guidance in effect prior to ASC 606	$	4,314		$	7,946
Impact of adoption of ASC 606		(2,779	)		(4,728	)
License revenue	$	1,535		$	3,218

The impact of adoption of ASC 606 on our net loss per share was as follows (in thousands):

	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Net loss per share using guidance in effect prior to ASC 606	$	(0.48	)	$	(0.98	)
Impact of adoption of ASC 606		0.03			0.09
Net loss per share	$	(0.51	)	$	(1.07	)

Our contract assets and liabilities changed during the period, as follows (in thousands):

	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Contract liability from the Amgen Agreement for the Co-Invest Option
Balance at beginning of period	$	12,500		$	18,750
Payments made for the Co-Invest Option		(6,250	)		(12,500	)
Balance at end of period	$	6,250		$	6,250

Contract asset from the 2016 Astellas Amendment
Balance at beginning of period	$	16,201		$	19,413
Cash received in advance of services performed		(1,735	)		(1,735	)
Reduction for services performed		(4,091	)		(7,303	)
Balance at end of period	$	10,375		$	10,375

Contract liability from the 2014 Astellas Amendment
Balance at beginning of period	$	3,336		$	6,288
Reduction for services performed		(1,454	)		(4,406	)
Balance at end of period	$	1,882		$	1,882

Research and Development Arrangements

6 Months Ended

Jun. 30, 2018

Research And Development [Abstract]

Research and Development Arrangements

Note 4 — Research and Development Arrangements

Amgen Inc. (“Amgen”)

We and Amgen continue activities related to novel small molecule therapeutics, including omecamtiv mecarbil, that activate cardiac muscle contractility for potential applications in the treatment of heart failure under the collaboration and option agreement between the Company and Amgen, as amended (the “Amgen Agreement”). We recognize research and development revenue for reimbursements from Amgen of both internal costs of certain full-time employee equivalents and other costs related to the Amgen Agreement.

We have exercised our option under the Amgen Agreement to co-invest $40.0 million in the Phase 3 development program of omecamtiv mecarbil in exchange for a total incremental royalty from Amgen of up to 4% on increasing worldwide sales of omecamtiv mecarbil outside Japan (the “Co-Invest Option”). We paid Amgen $12.5 million to fund the Co-Invest Option during the six months ended June 30, 2018. We paid the final $6.3 million to fully fund the Co-Invest Option in July 2018. Payments we made to fund the Co-Invest Option in 2016 and 2017 reduced research and development revenues in 2016 and 2017 by $1.3 million and $20.0 million, respectively.

Adoption of ASC 606

We determined that the Amgen Agreement was within the scope of ASC 606. As of January 1, 2018, all the performance obligations under the Amgen Agreement were complete. On January 1, 2018, we recognized a contract liability for $18.8 million with a corresponding increase in accumulated deficit for the Co-Invest Option. Payments in the six months ended June 30, 2018 reduced this contract liability to $6.3 million. Revenue recognized related to the Amgen Agreement during the first half of 2017 consisted of $0.9 million for research and development services, offset by our Co-Invest Option payment of $7.5 million in the first half of 2017.

We paid Amgen $6.3 million and $12.5 million for the Co-Invest Option during the three and six months ended June 30, 2018, respectively.

Under the Amgen Agreement, we are eligible to receive over $300.0 million in additional development milestone payments based on various clinical milestones, including the initiation of certain clinical studies, the submission of an application for marketing authorization for a drug candidate to certain regulatory authorities and the receipt of such approvals. Additionally, we are eligible to receive up to $300.0 million in commercial milestone payments provided certain sales targets are met. Due to the nature of drug development, including the inherent risk of development and approval of drug candidates by regulatory authorities, we cannot estimate if and when these milestone payments could be achieved or become due and, accordingly, we consider the milestone payments to be constrained and exclude the milestone payments from the transaction price.

Astellas Pharma Inc. (“Astellas”)

Cytokinetics and Astellas continue activities focused on the research, development, and commercialization of skeletal muscle activators, including reldesemtiv, as novel drug candidates for diseases and medical conditions associated with muscle weakness under the Amended and Restated License and Collaboration Agreement dated December 22, 2014, as amended (the “Astellas Agreement”).

We have recognized research and development revenue from Astellas for reimbursements of internal costs of certain full-time employee equivalents, supporting collaborative research and development programs, and of other costs related to those programs.

In 2014, we and Astellas amended and restated the license and collaboration agreement (the “2014 Astellas Amendment”) and expanded the objective of the collaboration to include spinal muscular atrophy (“SMA”) and potentially other neuromuscular indications for reldesemtiv and other fast skeletal muscle troponin activators (“FSTAs”); in connection therewith, Astellas paid us a $30.0 million non-refundable upfront license fee and a $15.0 million milestone payment. We determined at that time that the license for the expanded SMA rights did not have stand-alone value and the license and research and development services were a single unit of accounting and recognized revenue for these payments using the proportional performance model.

In 2016, we and Astellas amended the Astellas Agreement (the “2016 Astellas Amendment”) to expand the collaboration to include the development of reldesemtiv for the potential treatment of amyotrophic lateral sclerosis (“ALS”), as well as the possible development in ALS of other FSTAs previously licensed by us to Astellas, and Astellas paid us a $35.0 million non-refundable upfront amendment fee and an accelerated $15.0 million milestone payment for the initiation of the first Phase 2 clinical trial of reldesemtiv in ALS that was otherwise provided for in the Astellas Agreement, as if such milestone had been achieved upon the execution of the 2016 Astellas Amendment, and committed research and development consideration of $44.2 million, for total consideration of $94.2 million. We allocated the consideration to the license and to the research and development services, and recognized license revenue and research and development revenue using the proportional performance model.

Astellas’ Option on Tirasemtiv

In 2016, Astellas paid us a $15.0 million non-refundable option fee for the option for a global collaboration for the development and commercialization of tirasemtiv (the “Option on Tirasemtiv”). If Astellas exercises the Option on Tirasemtiv:

•

we will grant Astellas an exclusive license under a license and collaboration agreement to develop and commercialize tirasemtiv outside our commercialization territory of North America, Europe and other select countries (the “License on Tirasemtiv”). Each party would be primarily responsible for the further development of tirasemtiv in its territory and have the exclusive right to commercialize tirasemtiv in its territory.

•

we will receive an option exercise payment ranging from $25.0 million (if exercise occurs following receipt of data from VITALITY-ALS) to $80.0 million (if exercise occurs following receipt of FDA approval) and a milestone payment of $30.0 million from Astellas associated with our initiation of the open-label extension trial for tirasemtiv (VIGOR-ALS). If Astellas exercises the option after the defined review period following receipt of data, Astellas will at that time reimburse us for a share of any additional costs incurred after such review period.

•

the parties will share the future development costs of tirasemtiv in North America, Europe and certain other countries (with Cytokinetics bearing 75% of such shared costs and Astellas bearing 25% of such costs), and Astellas will be solely responsible for the development costs of tirasemtiv specific to its commercialization territory.

Contingent upon the successful development of tirasemtiv, we may receive from Astellas milestone payments. If tirasemtiv is commercialized, Astellas will pay us royalties on sales of tirasemtiv in Astellas’ territory, and we will pay Astellas royalties on sales of tirasemtiv in our territory.

While Astellas holds the Option on Tirasemtiv, we are responsible for and have final decision-making authority on the development of tirasemtiv at our expense. We concluded in 2016 that (i) we had no obligation to Astellas related to any development services pursuant to the Option on Tirasemtiv, (ii) the Option on Tirasemtiv was a substantive option and not a deliverable under the 2016 Astellas Amendment, and (iii) the $15.0 million payment was deferred revenue until the Option on Tirasemtiv is exercised or expires unexercised. The $15.0 million payment was included as deferred revenue in our non-current liabilities at December 31, 2017 (prior to adopting ASC 606).

Adoption of ASC 606

On January 1, 2018, in adopting ASC 606, we concluded: (i) that the original agreement with Astellas in 2013 was outside the scope of ASC 606, since all performance obligations thereunder were completed prior to entering into the 2014 Astellas Amendment and the 2014 Astellas Amendment was not an amendment of the original agreement, (ii) the 2014 Astellas Amendment is a separate agreement within the scope of ASC 606 with no effect on the ongoing accounting for the related license and research and development service deliverables and (iii) the 2016 Astellas Amendment is a separate agreement within the scope of ASC 606. In adopting ASC 606 we determined:

•

Our performance obligations were the delivery of the license and performance of research and development services;

•

The transaction price included the $50.0 million in non-refundable fees, the $35.6 million in committed research and development fees and the $15.0 million Astellas paid us for the Option on Tirasemtiv;

•

The consideration allocated to the license resulted in a contract asset of $19.4 million included in other current assets, with a corresponding decrease to accumulated deficit on January 1, 2018, and to be realized using the proportional performance model; and

•

Research services we perform under the Astellas Agreement in 2018 and beyond are a separate contract.

The transaction price above was allocated to the license (approximately $83 million) and to the services (approximately $18 million) based on their respective stand-alone prices.

Of the revenue we recognized in the first half of 2018, $4.4 million was included in the contract liability at the beginning of the period. This revenue includes the cumulative effect of changes made during the period in the estimated costs of research and development services to be incurred to satisfy the related deliverable.

Revenue from Astellas included (in thousands):

	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
Research and development revenues	$	4,680	$	4,942	$	8,265	$	6,388
License revenues		1,535		3,973		3,218	$	6,698
Total Revenue from Astellas	$	6,215	$	8,915	$	11,483	$	13,086

Of the transaction price allocated to the research and development services, approximately $4.6 million remains unrecognized at June 30, 2018.

We had accounts receivable from Astellas of $0.2 million at June 30, 2018 and no accounts receivable at December 31, 2017. Under the Astellas Agreement, additional research and early and late state development milestone payments for research and clinical milestones, including the initiation of certain clinical studies, the submission of an application for marketing authorization for a drug candidate to certain regulatory authorities and the commercial launch of collaboration products could total over $600.0 million and includes up to $95.0 million relating to reldesemtiv in non-neuromuscular indications, and over $100.0 million related to reldesemtiv in each of SMA, ALS and other neuromuscular indications. Additionally, $200.0 million in commercial milestones could be received under the Astellas Agreement provided certain sales targets are met. We are eligible to receive up to $2.0 million in research milestone payments under the collaboration for each future potential drug candidate. Due to the nature of drug development, including the inherent risk of development and approval of drug candidates by regulatory authorities, it is not possible to estimate if and when these milestone payments could be achieved or become due, and accordingly, are constrained and not included in the transaction price.

Cash Equivalents and Investments

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Cash Equivalents and Investments

Note 5 — Cash Equivalents and Investments

The amortized cost and fair value of cash equivalents and available for sale investments at June 30, 2018 and December 31, 2017 were as follows (in thousands):

	June 30, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	37,992	$	—	$	—		$	37,992
U.S. Treasury securities		91,000		1		(108	)		90,893
Agency bonds		39,634		—		(5	)		39,629
Commercial paper		49,160		6		(3	)		49,163
Corporate obligations		12,619		—		(15	)		12,604
	$	230,404	$	7	$	(130	)	$	230,281

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents	$	111,501	$	—	$	—		$	111,501
Short-term investments	$	143,895	$	—	$	(210	)	$	143,685
Long-term investments	$	16,538	$	—	$	(20	)	$	16,518

Investments available for sale at June 30, 2018 excludes an investment in equity with a fair value and unrealized gain of $0.7 million. At June 30, 2018, there were no investments that had been in a continuous unrealized loss position for 12 months or longer.

Interest income was $1.1 million and $2.0 million for the three and six months ended June 30 2018 and $0.6 million and $1.0 million for the three and six months ended June 30, 2017, respectively.

Fair Value Measurements

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

Note 6 — Fair Value Measurements

We value our financial assets and liabilities at fair value, defined as the price that would be received for assets when sold or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We utilize market data or assumptions that we believe market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated or generally unobservable.

We primarily apply the market approach for recurring fair value measurements and endeavors to utilize the best information reasonably available. Accordingly, we use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible, and consider the security issuers’ and the third-party issuers’ credit risk in our assessment of fair value.

We classify fair value based on the observability of those inputs using a hierarchy that prioritizes the inputs used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement):

Level 1 — Observable inputs, such as quoted prices in active markets for identical assets or liabilities;

Level 2 — Inputs, other than the quoted prices in active markets, that are observable either directly or through corroboration with observable market data; and

Level 3 — Unobservable inputs, for which there is little or no market data for the assets or liabilities, such as internally-developed valuation models.

Fair value of financial assets:

Financial assets measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 are classified in the table below in one of the three categories described above (in thousands):

	June 30, 2018
	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Assets At Fair Value
Assets:
Money market funds	$	37,992	$	—	$	—	$	37,992
U.S. Treasury securities		90,893		—		—		90,893
Agency bonds		—		39,629		—		39,629
Commercial paper		—		49,163		—		49,163
Corporate obligations		—		12,604		—		12,604
	$	128,885	$	101,396	$	—	$	230,281

	December 31, 2017
	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Assets At Fair Value
Assets:
Money market funds	$	51,001	$	—	$	—	$	51,001
U.S. Treasury securities		165,801		—		—		165,801
Agency bonds		—		54,329		—		54,329
Equity securities		573		—		—		573
	$	217,375	$	54,329	$	—	$	271,704

The carrying amount of our accounts receivable and accounts payable approximates fair value due to the short-term nature of these instruments.

Fair value of financial liabilities:

As of June 30, 2018 and December 31, 2017, the fair value of the long-term debt approximated its carrying value of $32.4 million and $31.8 million, respectively, because it is carried at a market observable interest rate, which is considered Level 2.

As of June 30, 2018, the fair value of liability related to the sale of future royalties is based on our current estimates of future royalties expected to be paid to RPI Finance Trust (“RPI”), an entity related to Royalty Pharma, over the life of the arrangement, which are considered Level 3 (See Note 9 – “Liability Related to Sale of Future Royalties”).

There were no transfers between Level 1, Level 2, and Level 3 during the periods presented.

- 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

Balance Sheet Components

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Components

Note 7 — Balance Sheet Components

Accrued liabilities were as follows (in thousands):

	June 30, 2018		December 31, 2017
Accrued liabilities:
Research and development services	$	10,290	$	9,436
Compensation related		4,527		6,260
Other accrued expenses		1,273		1,696
Total accrued liabilities	$	16,090	$	17,392

Long-Term Debt

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Long-Term Debt

Note 8 — Long-Term Debt

We have a loan and security agreement (the “Loan Agreement”) with Oxford Finance LLC (“Oxford”) and Silicon Valley Bank (“SVB”) (Oxford and SVB, collectively the “Lenders”) to fund our working capital and other general corporate needs. Our Long-term debt and unamortized debt discount balances are as follows (in thousands):

	June 30, 2018			December 31, 2017
Notes payable, gross	$	32,000		$	32,000
Less: Unamortized debt discount and issuance costs		(41	)		(325	)
Accretion of final payment fee		406			102
Carrying value of notes payable		32,365			31,777
Less: Current portion of long-term debt		(1,703	)		—
Long-term debt	$	30,662		$	31,777

Payments on the notes payable will be interest only through May 2019, followed by 41 months of monthly payments of interest and principal. We are required to make a final payment upon loan maturity of 6.5% of the notes payable, which we accrete over the life of the notes payable. The interest rate under the Amended Loan Agreement is the greater of (a) 8.05% or (b) the sum of 6.81% plus the 30-day U.S. LIBOR rate.

The Loan Agreement contains customary representations and warranties and customary affirmative and negative covenants applicable to us and includes customary events of default, including but not limited to the nonpayment of principal or interest, violations of covenants and material adverse changes. Upon an event of default, the Lenders may, among other things, accelerate the loans and foreclose on the collateral. Our obligations under the Loan Agreement are secured by substantially all our current and future assets, other than our intellectual property.

Interest expense was $0.8 million and $0.8 million for the three months ended June 30, 2018 and 2017, respectively and $1.8 million and $1.5 million for the six months ended June 30, 2018 and 2017, respectively. The effective interest rate on the Loan Agreement, including the amortization of the debt discount and issuance cost, and the accretion of the final payment, was 8.9% at June 30, 2018.

Minimum payments under the Loan Agreement are (in thousands):

2018	$	2,615
2019		7,963
2020		11,187
2021		10,417
2022		10,176
Total minimum payments		42,358
Less: Interest and final payment		(10,358	)
Notes payable, gross	$	32,000

Liability Related to Sale of Future Royalties	6 Months Ended
Liability Related to Sale of Future Royalties	Jun. 30, 2018
Deferred Revenue Disclosure [Abstract]
Liability Related to Sale of Future Royalties	Note 9 - Liability Related to Sale of Future Royalties In February 2017, we entered into a Royalty Purchase Agreement (the “Royalty Agreement”), under which we sold a portion of our right to receive royalties on potential net sales of omecamtiv mecarbil (and potentially other compounds with the same mechanism of action) under the Amgen Agreement to RPI for a payment of $90.0 million (the “Royalty Monetization”). The Royalty Monetization is non-refundable, even if omecamtiv mecarbil is never commercialized. Concurrently, we entered into a Common Stock Purchase Agreement with RPI through which RPI purchased 875,676 shares of our common stock for $10.0 million (the “RPI Common Stock”). We concluded that there are two units of accounting for the Royalty Monetization and the RPI Common Stock: (1) the Liability related to sale of future royalties and (2) the sale of the RPI Common Stock. We determined the fair value for the Liability related to sale of future royalties at the time of the Royalty Monetization to be $96.7 million, with an effective annual non-cash interest rate of 17% based on our estimate of the cash flows to be received over the life of the Royalty Agreement. We further determined that the fair value of the RPI Common Stock was $8.1 million at the time we entered into the Royalty Agreement. We allocated the consideration of $100.0 million and related transaction costs of $1.8 million on a relative fair value basis to the liability for $92.3 million and the common stock for $7.7 million. We continue to accrete the Liability related to sale of future royalties using the interest method with an annual pre-tax interest rate of 17%. The transaction costs are amortized to non-cash interest expense over the estimated term of the Royalty Agreement. As of December 31, 2017, we determined the fair value at $131.6 million, after considering the new statutory effective tax rate of 21% in 2018. We recognized $4.3 million and $3.7 million in non-cash interest expense in the three months ended June 30, 2018 and 2017, respectively, and $8.5 million and $6.0 million in non-cash interest expense in the six months ended June 30, 2018 and 2017, related to the Royalty Agreement.

Stockholders' Equity	6 Months Ended
Stockholders' Equity	Jun. 30, 2018
Equity [Abstract]
Stockholders' Equity	Note 10 — Stockholders’ Equity Equity Incentive Plan At December 31, 2017, we had outstanding 171,250 Performance Units with an award date fair value per unit of $7.00. The performance criteria for these Performance Units were met in 2017 and these units vested in March 2018. As of June 30, 2018, 2.2 million authorized shares were available for grant under the 2004 Equity Plan. Warrants At June 30, 2018, we had outstanding warrants to purchase 100,106 shares of our common stock, issued pursuant to the Loan Agreement, with a weighted average exercise price of $6.74 per share.

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 11 — Commitments and Contingencies Commitments Operating Lease: Our non-cancelable operating lease for our facilities expires in 2021 and includes rental payments on a graduated scale and our payment of certain operating expenses. We recognize rent expense on a straight-line basis over the lease period. Rent expense was $1.3 million and $0.9 million for the three months ended June 30, 2018 and 2017, respectively, and $2.5 million and $1.8 million for the six months ended June 30, 2018 and 2017, respectively. Contingencies In the ordinary course of business, we may provide indemnifications of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters, including, but not limited to, losses arising out of our breach of such agreements, services to be provided by or on behalf of us, or from intellectual property infringement claims made by third parties. In addition, we have indemnification agreements with our directors and certain of our officers and employees that will require us, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. We maintain director and officer insurance, which may cover certain liabilities arising from our obligation to indemnify our directors and certain of our officers and employees, and former officers and directors in certain circumstances. We maintain product liability insurance and comprehensive general liability insurance, which may cover certain liabilities arising from our indemnification obligations. It is not possible to determine the maximum potential amount of exposure under these indemnification obligations due to the limited history of prior indemnification claims and the unique facts and circumstances involved in each particular indemnification obligation. Such indemnification obligations may not be subject to maximum loss clauses. We are not currently aware of any matters that could have a material adverse effect on our financial position, results of operations or cash flows.

Organization and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Our condensed consolidated financial statements include the accounts of Cytokinetics and our wholly-owned subsidiary. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. The financial statements include all adjustments (consisting only of normal recurring adjustments) that management believes are necessary for the fair statement of our financial information. These interim results are not necessarily indicative of results to be expected for the full fiscal year or any future interim period. The balance sheet at December 31, 2017 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. The financial statements and related disclosures have been prepared with the presumption that users of the interim financial statements have read or have access to the audited financial statements for the preceding fiscal year. Accordingly, these financial statements should be read in conjunction with the audited financial statements and notes thereto contained in the Company’s Form 10-K for the year ended December 31, 2017, as filed with the SEC.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the condensed consolidated financial statements and reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, investments, accrued research and development expenses, other long-lived assets, stock-based compensation and the valuation of deferred tax assets. We base our estimates on our historical experience and also on assumptions that we believe are reasonable; however, actual results could significantly differ from those estimates.
Revenue Recognition – Adoption of Revenue from Contracts with Customers ASC 606	Revenue Recognition – Adoption of Revenue from Contracts with Customers ASC 606 On January 1, 2018, we adopted Revenue from Contracts with Customers (ASC 606), using the modified retrospective method. On January 1, 2018, for contracts within the scope of ASC 606, we recognized a contract asset or liability and reduced our accumulated deficit by $15.7 million for the effect of adopting ASC 606 and did not revise our prior period financial statements. Pursuant to ASC 606, to recognize revenue from a contract with a customer, we: (i) identify our contracts with our customers; (ii) identify our distinct performance obligations in each contract; (iii) determine the transaction price of each contract; (iv) allocate the transaction price to the performance obligations; and (v) recognize revenue as we satisfy our performance obligations. At contract inception, we assess the goods or services promised within each contract and assess whether each promised good or service is distinct and determine those that are performance obligations. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaborative Arrangements We enter into collaborative arrangements with partners that typically include payment to us for one of more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; and (iii) royalties on net sales of licensed products. Each of these payments results in collaboration or other revenues. Where a portion of non-refundable up-front fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. As part of the accounting for these arrangements, we must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation. The stand-alone selling price may include such items as, forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, to determine the transaction price to allocate to each performance obligation. For our collaboration agreements that include more than one performance obligation, such as a license combined with a commitment to perform research and development services, we make judgments to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. We evaluate our progress each reporting period and, if necessary, adjust the measure of a performance obligation and related revenue recognition. License Fees: If a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front license fees. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments: We use judgement to determine whether a milestone is considered probable of being reached. Using the most likely amount method, we include the value of a milestone payment in the consideration for a contract at inception if we then conclude achieving the milestone is more likely than not. Otherwise, we exclude the value of a milestone payment from contract consideration at inception and recognize revenue for a milestone at a later date, when we judge that it is more likely than not that the milestone will be achieved. If we conclude it is probable that a significant revenue reversal would not occur, the associated milestone is included in the transaction price. We then allocate the transaction price to each performance obligation on a relative stand-alone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, we re-evaluate the probability of achievement of such milestones and any related constraint, and if necessary, adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration and other revenues and earnings in the period of adjustment. Royalties: For contracts that include sales-based royalties, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied. To date, we have not recognized any royalty revenues resulting from contracts.
Income Taxes	Income Taxes We account for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. We establish valuation allowances when necessary to reduce deferred tax assets to the amounts expected to be realized. We recognize uncertain tax positions taken or expected to be taken on a tax return. Tax positions are initially recognized when it is more likely than not that the position will be sustained upon examination by the tax authorities. We measure our tax positions as the largest amount of tax benefit that is more likely than not of being realized upon ultimate settlement with the tax authority assuming full knowledge of the position and relevant facts. We recognize interest accrued related to unrecognized tax benefits and penalties as income tax expense. In December 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017. Staff Accounting Bulletin No. 118 ("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. We continue to analyze certain provisions of the Act including the application of new executive compensation limitation provisions under Internal Revenue Section 162(m). These items are subject to revisions from further analysis of the Tax Act and interpretation of any additional guidance issued by the U.S. Treasury Department, IRS, FASB, and other standard-setting and regulatory bodies. We did not record a provision for income tax for three and six months ended June 30, 2018 because we expect to report a net tax loss for the year ending December 31, 2018.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, ‘Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments. ASU 2016-13 changes the impairment model for most financial assets and certain other instruments and is effective for annual and interim reporting periods beginning after December 15, 2019. We do not expect the adoption of ASU 2016-13 to have a material impact on our financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 requires us to record right-of-use asset and lease liability on the statement of financial position for operating leases with lease terms of more than 12 months and is effective for annual and interim reporting periods beginning on or after December 15, 2018. We expect to adopt this standard beginning in 2019 using the modified retrospective approach. We do not expect that this standard will have a material impact on our results of operations, but we do expect that upon adoption, it will have a material impact on our assets and liabilities. The primary effect of adoption will be the requirement to record right-of-use assets and corresponding lease obligations for current operating leases with lease terms of more than 12 months.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References + Details

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Instruments Excluded from Diluted Net Loss Per Share

We excluded the following from diluted net loss per share because inclusion would have been antidilutive (in thousands):

	Six Months Ended
	June 30, 2018		June 30, 2017
Options to purchase common stock		5,421		6,170
Warrants to purchase common stock		100		310
Restricted Stock and Performance units		581		461
Shares issuable related to the ESPP		28		18
		6,130		6,959

Revenue Recognition (Tables)

6 Months Ended

Jun. 30, 2018

Revenue Recognition Multiple Deliverable Arrangements [Line Items]

Schedule of Revenue Affected by Adopting ASC 606

Our revenue for the three and six months ended June 30, 2018 was affected by adopting ASC 606 as follows (in thousands):

	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Research and development revenue using guidance in effect prior to ASC 606	$	70		$	(1,334	)
Impact of adoption of ASC 606		4,610			9,599
Research and development revenue	$	4,680		$	8,265

License revenue using guidance in effect prior to ASC 606	$	4,314		$	7,946
Impact of adoption of ASC 606		(2,779	)		(4,728	)
License revenue	$	1,535		$	3,218

Schedule of Changes in Contract Assets and Liabilities

Our contract assets and liabilities changed during the period, as follows (in thousands):

	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Contract liability from the Amgen Agreement for the Co-Invest Option
Balance at beginning of period	$	12,500		$	18,750
Payments made for the Co-Invest Option		(6,250	)		(12,500	)
Balance at end of period	$	6,250		$	6,250

Contract asset from the 2016 Astellas Amendment
Balance at beginning of period	$	16,201		$	19,413
Cash received in advance of services performed		(1,735	)		(1,735	)
Reduction for services performed		(4,091	)		(7,303	)
Balance at end of period	$	10,375		$	10,375

Contract liability from the 2014 Astellas Amendment
Balance at beginning of period	$	3,336		$	6,288
Reduction for services performed		(1,454	)		(4,406	)
Balance at end of period	$	1,882		$	1,882

Accounting Standards Update 2014-09 [Member]

Revenue Recognition Multiple Deliverable Arrangements [Line Items]

Schedule of Revenue Impact of Adoption of ASC 606 on Net Loss Per Share

The impact of adoption of ASC 606 on our net loss per share was as follows (in thousands):

	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Net loss per share using guidance in effect prior to ASC 606	$	(0.48	)	$	(0.98	)
Impact of adoption of ASC 606		0.03			0.09
Net loss per share	$	(0.51	)	$	(1.07	)

Research and Development Arrangements (Tables)

6 Months Ended

Jun. 30, 2018

Astellas [Member]

Summary of Research and Development Revenue

Revenue from Astellas included (in thousands):

	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
Research and development revenues	$	4,680	$	4,942	$	8,265	$	6,388
License revenues		1,535		3,973		3,218	$	6,698
Total Revenue from Astellas	$	6,215	$	8,915	$	11,483	$	13,086

Cash Equivalents and Investments (Tables)

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Amortized Cost and Fair Value of Cash Equivalents and Available for Sale Investments

The amortized cost and fair value of cash equivalents and available for sale investments at June 30, 2018 and December 31, 2017 were as follows (in thousands):

	June 30, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	37,992	$	—	$	—		$	37,992
U.S. Treasury securities		91,000		1		(108	)		90,893
Agency bonds		39,634		—		(5	)		39,629
Commercial paper		49,160		6		(3	)		49,163
Corporate obligations		12,619		—		(15	)		12,604
	$	230,404	$	7	$	(130	)	$	230,281

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents	$	111,501	$	—	$	—		$	111,501
Short-term investments	$	143,895	$	—	$	(210	)	$	143,685
Long-term investments	$	16,538	$	—	$	(20	)	$	16,518

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

Financial assets measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 are classified in the table below in one of the three categories described above (in thousands):

	June 30, 2018
	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Assets At Fair Value
Assets:
Money market funds	$	37,992	$	—	$	—	$	37,992
U.S. Treasury securities		90,893		—		—		90,893
Agency bonds		—		39,629		—		39,629
Commercial paper		—		49,163		—		49,163
Corporate obligations		—		12,604		—		12,604
	$	128,885	$	101,396	$	—	$	230,281

	December 31, 2017
	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Assets At Fair Value
Assets:
Money market funds	$	51,001	$	—	$	—	$	51,001
U.S. Treasury securities		165,801		—		—		165,801
Agency bonds		—		54,329		—		54,329
Equity securities		573		—		—		573
	$	217,375	$	54,329	$	—	$	271,704

Balance Sheet Components (Tables)

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of Accrued Liabilities

Accrued liabilities were as follows (in thousands):

	June 30, 2018		December 31, 2017
Accrued liabilities:
Research and development services	$	10,290	$	9,436
Compensation related		4,527		6,260
Other accrued expenses		1,273		1,696
Total accrued liabilities	$	16,090	$	17,392

Long-Term Debt (Tables)

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Schedule Of Long Term Debt And Unamortized Debt Discount

Our Long-term debt and unamortized debt discount balances are as follows (in thousands):

	June 30, 2018			December 31, 2017
Notes payable, gross	$	32,000		$	32,000
Less: Unamortized debt discount and issuance costs		(41	)		(325	)
Accretion of final payment fee		406			102
Carrying value of notes payable		32,365			31,777
Less: Current portion of long-term debt		(1,703	)		—
Long-term debt	$	30,662		$	31,777

Schedule of Future Minimum Payments under Loan

Minimum payments under the Loan Agreement are (in thousands):

2018	$	2,615
2019		7,963
2020		11,187
2021		10,417
2022		10,176
Total minimum payments		42,358
Less: Interest and final payment		(10,358	)
Notes payable, gross	$	32,000

Organization and Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($) Obligation	Jun. 30, 2018 USD ($) Obligation	Dec. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit incurred	$ (688,222,000)	$ (688,222,000)	$ (646,081,000)
Cash requirements term		12 months
Effective tax rate		21.00%	34.00%
Provision for income taxes	$ 0	$ 0
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of performance obligation \| Obligation	1	1
Accounting Standards Update 2014-09 [Member] \| Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit incurred				$ (15,700,000)
Accounting Standards Update 2016-02 [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating leases with lease terms	12 months	12 months

Net Loss Per Share - Instruments Excluded from Diluted Net Loss Per Share (Detail) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	6,130	6,959
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	5,421	6,170
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	100	310
Restricted Stock and Performance Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	581	461
ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	28	18

Revenue Recognition - Schedule of Revenue Affected by Adopting ASC 606 (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research and development revenues	$ 4,680		$ 8,265
License Revenues [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenues	1,535	$ 4,942	3,218	$ 6,388
Calculated Under Revenue Guidance in Effect Before Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research and development revenues	70		(1,334)
Calculated Under Revenue Guidance in Effect Before Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member] \| License Revenues [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenues	4,314		7,946
Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research and development revenues	4,610		9,599
Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member] \| License Revenues [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenues	$ (2,779)		$ (4,728)

Revenue Recognition - Schedule of Revenue Impact of Adoption of ASC 606 on Net Loss Per Share (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net loss per share - basic and diluted	$ (0.51)	$ (0.60)	$ (1.07)	$ (1.22)
Guidance in Effect Prior Topic to ASC 606 [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net loss per share - basic and diluted	(0.48)		(0.98)
Impact of Adoption of ASC 606 [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net loss per share - basic and diluted	$ 0.03		$ 0.09

Revenue Recognition - Schedule of Changes in Contract Assets and Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Balance at beginning of period		$ 0
Balance at beginning of period		0
Balance at end of period	$ 8,132	8,132
Balance at end of period	10,375	10,375
Amgen Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Balance at beginning of period	12,500	18,750
Payments made for the Co-Invest Option	(6,250)	(12,500)
Balance at end of period	6,250	6,250
2016 Astellas Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Balance at beginning of period	16,201	19,413
Cash received in advance of services performed	(1,735)	(1,735)
Reduction for services performed	(4,091)	(7,303)
Balance at end of period	10,375	10,375
2014 Astellas Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Balance at beginning of period	3,336	6,288
Reduction for services performed	(1,454)	(4,406)
Balance at end of period	$ 1,882	$ 1,882

Research and Development Arrangements - Additional Information (Details) - USD ($)			3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 27, 2018	Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Mar. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accumulated deficit incurred			$ (688,222,000)		$ (688,222,000)		$ (646,081,000)
Reduction in contract liability					$ (10,618,000)	$ 0
Percentage of shared costs					75.00%
Deferred revenue, current			0		$ 0		9,572,000
Research and development			21,582,000	$ 19,809,000	43,717,000	39,098,000
Contract assets			10,375,000		10,375,000		0
Contract liabilities			8,132,000		8,132,000		0
Accounts receivable			236,000		236,000		1,112,000
2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable option fee								$ 15,000,000
2016 Astellas Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract with Customer, Liability, Revenue Recognized			1,735,000		1,735,000
Contract assets			10,375,000		10,375,000		19,413,000			$ 16,201,000
Maximum [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research milestone payments					2,000,000
Maximum [Member] \| 2016 Astellas Amendment [Member] \| Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement					200,000,000
Accounting Standards Update 2014-09 [Member] \| Amgen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Pre-commercialization milestone payments eligible to receive			300,000,000		300,000,000
Accounting Standards Update 2014-09 [Member] \| Maximum [Member] \| Amgen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Commercialization milestone payments eligible to receive			300,000,000		300,000,000
Accounting Standards Update 2014-09 [Member] \| Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accumulated deficit incurred		$ (15,700,000)
Contract liabilities			4,400,000		4,400,000
Accounting Standards Update 2014-09 [Member] \| Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accumulated deficit incurred		19,400,000
Non-refundable fees		50,000,000
Research and development		35,600,000
Contract assets		19,400,000
License transaction price		83,000,000
Services transaction price		18,000,000
Amgen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Co-invest option exercised amount					$ 40,000,000
Percentage of incremental royalty receivable on annual net sales					4.00%
Co-invest option payment					$ 12,500,000
Reduction in research and development revenue due to payments made to fund the Co-Invest Option					0		20,000,000	1,300,000
Amgen [Member] \| Accounting Standards Update 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Co-invest option payment			6,300,000		12,500,000
Reduction in contract liability					(6,300,000)
Revenue from Contract with Customer, Excluding Assessed Tax						900,000
Co-invest option payment						7,500,000
Amgen [Member] \| Accounting Standards Update 2014-09 [Member] \| Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract with Customer, Liability, Revenue Recognized		18,800,000
Accumulated deficit incurred		$ (18,800,000)
Amgen [Member] \| Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Co-invest option payment	$ 6,300,000
Astellas [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			4,680,000	$ 4,942,000	$ 8,265,000	$ 6,388,000
Percentage of shared costs					25.00%
Accounts receivable			200,000		$ 200,000		0
Astellas [Member] \| 2014 Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received									$ 30,000,000
Amount received as milestone payment									$ 15,000,000
Astellas [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount received as milestone payment								15,000,000
Revenue recognition, Non-refundable upfront amendment fee								35,000,000
Revenue Recognition over Performance Period								44,200,000
Allocated Consideration								$ 94,200,000
Astellas [Member] \| 2016 Astellas Agreement [Member] \| Tirasemtiv Option [Member] \| Tirasemtiv License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized for milestones achieved							15,000,000
Astellas [Member] \| Maximum [Member] \| 2016 Astellas Amendment [Member] \| Non Neuromuscular Indications
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement					95,000,000
Astellas [Member] \| Maximum [Member] \| 2016 Astellas Amendment [Member] \| Tirasemtiv Option [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount received as milestone payment					30,000,000
Astellas [Member] \| Maximum [Member] \| 2016 Astellas Amendment [Member] \| Tirasemtiv Option [Member] \| Clearing Service [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax					80,000,000
Astellas [Member] \| Minimum [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement					600,000,000
Astellas [Member] \| Minimum [Member] \| 2016 Astellas Amendment [Member] \| SMA and Other Neuromuscular Indications [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement					100,000,000
Astellas [Member] \| Minimum [Member] \| 2016 Astellas Amendment [Member] \| Tirasemtiv Option [Member] \| Clearing Service [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax					25,000,000
Astellas [Member] \| Calculated Under Revenue Guidance in Effect Before Topic 606 [Member] \| 2016 Astellas Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, current							$ 15,000,000
Astellas [Member] \| Accounting Standards Update 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Unrecognized transaction price			$ 4,600,000		$ 4,600,000

Research and Development Arrangements - Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total Revenue	$ 6,215	$ 3,053	$ 11,483	$ 7,206
Astellas [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development revenues	4,680	4,942	8,265	6,388
Total Revenue	6,215	8,915	11,483	13,086
Astellas [Member] \| License Revenues [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
License revenues	$ 1,535	$ 3,973	$ 3,218	$ 6,698

Cash Equivalents and Investments - Amortized Cost and Fair Value of Cash Equivalents and Available for Sale Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Cash And Cash Equivalents [Line Items]
Amortized Cost	$ 46,955	$ 125,206
Amortized Cost	230,404
Unrealized Gains	7
Unrealized Losses	(130)
Fair Value	230,281
Cash Equivalents [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost		111,501
Unrealized Gains		0
Unrealized Losses		0
Fair Value		111,501
Short-term Investments [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost		143,895
Unrealized Gains		0
Unrealized Losses		(210)
Fair Value		143,685
Long-term Investments [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost		16,538
Unrealized Gains		0
Unrealized Losses		(20)
Fair Value		$ 16,518
Money Market Funds [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	37,992
Unrealized Gains	0
Unrealized Losses	0
Fair Value	37,992
U.S. Treasury Securities [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	91,000
Unrealized Gains	1
Unrealized Losses	(108)
Fair Value	90,893
Agency Bonds [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	39,634
Unrealized Gains	0
Unrealized Losses	(5)
Fair Value	39,629
Commercial Paper [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	49,160
Unrealized Gains	6
Unrealized Losses	(3)
Fair Value	49,163
Corporate Obligations [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	12,619
Unrealized Gains	0
Unrealized Losses	(15)
Fair Value	$ 12,604

Cash Equivalents and Investments - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash And Cash Equivalents [Abstract]
Investment in equity with a fair value and unrealized gain	$ 700,000		$ 700,000
Investments in continuous unrealized loss position for 12 months or longer	0		0
Interest income	$ 1,100,000	$ 600,000	$ 2,000,000	$ 1,000,000

Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Long-term debt, fair value	$ 32,400,000	$ 31,800,000
Fair value of liabilities transferred from level 1 to level 2	0
Fair value of liabilities transferred from level 2 to level 1	0
Fair value of liabilities transferred into level 3	0
Fair value of liabilities transferred from level 3	$ 0

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accrued liabilities:
Research and development services	$ 10,290	$ 9,436
Compensation related	4,527	6,260
Other accrued expenses	1,273	1,696
Total accrued liabilities	$ 16,090	$ 17,392

Long-Term Debt - Schedule of Long Term Debt and Unamortized Debt Discount (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Notes payable, gross	$ 32,000	$ 32,000
Less: Unamortized debt discount and issuance costs	(41)	(325)
Accretion of final payment fee	406	102
Carrying value of notes payable	32,365	31,777
Less: Current portion of long-term debt	(1,703)	0
Long-term debt, net	$ 30,662	$ 31,777

Long-Term Debt - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Installment	Jun. 30, 2017 USD ($)
Debt Instrument [Line Items]
Loan repayment terms			Payments on the notes payable will be interest only through May 2019, followed by 41 months of monthly payments of interest and principal.
Number of installments description			41 months of monthly payments of interest and principal
Number of installments \| Installment			41
Final payment fee percentage			6.50%
Debt instrument, applicable interest rate for scenario 1	8.05%		8.05%
Debt instrument, base interest rate for scenario 2	6.81%		6.81%
Interest rate description			The interest rate under the Amended Loan Agreement is the greater of (a) 8.05% or (b) the sum of 6.81% plus the 30-day U.S. LIBOR rate.
Interest expense	$ 898	$ 782	$ 1,761	$ 1,540
Oxford and Silicon Valley Bank [Member] \| Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Interest expense	$ 800	$ 800	$ 1,800	$ 1,500
Effective interest rate on the amounts borrowed under the Agreement	8.90%		8.90%

Long-Term Debt - Schedule of Future Minimum Payments under Loan Agreement (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Carrying value of notes payable	$ 32,365	$ 31,777
Long-term debt, alternative
Carrying value of notes payable	32,365	31,777
Notes payable, gross	32,000	$ 32,000
Loan and Security Agreement [Member] \| Oxford and Silicon Valley Bank [Member]
Debt Instrument [Line Items]
2018	2,615
2019	7,963
2020	11,187
2021	10,417
2022	10,176
Carrying value of notes payable	42,358
Long-term debt, alternative
Carrying value of notes payable	42,358
Less: Interest and final payment	(10,358)
Notes payable, gross	$ 32,000

Liability Related to Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Feb. 28, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Proceeds from issuance of common stock				$ 0	$ 112,232
Allocated Consideration				100,000
Transaction costs incurred in connection with the Royalty Monetization and RPI Common stock				1,800
Non-cash interest expense recognized				$ 8,467	6,036
Effective tax rate				21.00%		34.00%
Liability Related to Sale of Future Royalties [Member]
Liability Related to Sale of Future Royalties [Line Items]
Allocated Consideration				$ 92,300
Common Stock [Member]
Liability Related to Sale of Future Royalties [Line Items]
Allocated Consideration				7,700
Royalty Purchase Agreement [Member]
Liability Related to Sale of Future Royalties [Line Items]
Cash payment under Royalty Agreement	$ 90,000
Common stock, shares issued in period	875,676
Proceeds from issuance of common stock	$ 10,000
Fair value for the liability related to sale of future royalties		$ 131,600		$ 131,600
Effective annual non-cash interest rate in calculating liability related to sale of future royalties		17.00%		17.00%
Common stock fair value				$ 8,100
Annual pre-tax interest rate in calculating liability related to sale of future royalties		17.00%		17.00%
Non-cash interest expense recognized		$ 4,300	$ 3,700	$ 8,500	$ 6,000
Effective tax rate				21.00%
Royalty Purchase Agreement [Member] \| Scenario Previously Reported [Member]
Liability Related to Sale of Future Royalties [Line Items]
Fair value for the liability related to sale of future royalties		$ 96,700		$ 96,700

Stockholders' Equity - Additional Information (Detail) - $ / shares	1 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding warrants		100,106
Outstanding warrants, weighted average exercise price		$ 6.74
2004 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant of options		2.2
Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units outstanding			171,250
Award date fair value per unit			$ 7.00
Units vested	171,250

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Non-cancelable operating lease expiration year			2021
Rent expense	$ 1.3	$ 0.9	$ 2.5	$ 1.8

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	$ 230,281	$ 271,704
Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	128,885	217,375
Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	101,396	54,329
Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	37,992	51,001
Money Market Funds [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	37,992	51,001
Money Market Funds [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Money Market Funds [Member] \| Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
U.S. Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	90,893	165,801
U.S. Treasury Securities [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	90,893	165,801
U.S. Treasury Securities [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
U.S. Treasury Securities [Member] \| Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Agency Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	39,629	54,329
Agency Bonds [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Agency Bonds [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	39,629	54,329
Agency Bonds [Member] \| Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	49,163
Commercial Paper [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0
Commercial Paper [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	49,163
Commercial Paper [Member] \| Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0
Corporate Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	12,604
Corporate Obligations [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	0
Corporate Obligations [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	12,604
Corporate Obligations [Member] \| Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value	$ 0
Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value		573
Equity Securities [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value		573
Equity Securities [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value		0
Equity Securities [Member] \| Fair Value Measurements Using Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets at fair value		$ 0