Cytokinetics (CYTK) 10-K 6 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Feb. 23, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	CYTK
Entity Registrant Name	CYTOKINETICS INC
Entity Central Index Key	1,061,983
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		41,729,549
Entity Public Float			$ 375.5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 66,874	$ 65,076
Short-term investments	89,375	46,366
Related party accounts receivable	24	12
Prepaid and other current assets	2,360	1,653
Total current assets	158,633	113,107
Long-term investments	7,672	179
Property and equipment, net	3,637	1,751
Other assets	200	200
Total assets	170,142	115,237
Current liabilities:
Accounts payable	4,236	2,238
Accrued liabilities	18,047	8,421
Deferred revenue, current	8,060	20,858
Current portion of long-term debt	2,500	0
Short-term portion of deferred rent and interest payable	415	132
Total current liabilities	33,258	31,649
Long-term debt	27,381	14,639
Deferred revenue, non-current	15,000	0
Long-term portion of deferred rent	142	359
Total liabilities	75,781	46,647
Commitments and contingencies (Note 10)
Stockholders' equity:
Issued and outstanding: Series A Convertible Preferred Stock - zero shares at December 31, 2016 and December 31, 2015	0	0
Common stock, $0.001 par value: Authorized: 163,000,000 shares at December 31, 2016 and 81,500,000 shares at December 31, 2015; Issued and outstanding: 40,646,595 shares at December 31, 2016 and 39,581,692 shares at December 31, 2015	41	40
Additional paid-in capital	612,474	603,145
Accumulated other comprehensive income	137	149
Accumulated deficit	(518,291)	(534,744)
Total stockholders' equity	94,361	68,590
Total liabilities and stockholders' equity	$ 170,142	$ 115,237

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	163,000,000	81,500,000
Common stock, shares issued	40,646,595	39,581,692
Common stock, shares outstanding	40,646,595	39,581,692

Consolidated Statement of Opera

Consolidated Statement of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Research and development revenues from related parties, net	$ 42,994	$ 14,665	$ 19,538
Research and development, grant and other revenues	1,242	75	17,566
License revenues from related parties	62,171	13,918	0
License revenues	0	0	9,836
Total revenues	106,407	28,658	46,940
Operating expenses:
Research and development	59,897	46,398	44,426
General and administrative	27,823	19,667	17,268
Total operating expenses	87,720	66,065	61,694
Operating income (loss)	18,687	(37,407)	(14,754)
Interest expense	(2,698)	(268)	0
Interest and other income, net	464	174	108
Income (loss) before income taxes	16,453	(37,501)	(14,646)
Income tax benefit	0	0	0
Net income (loss)	$ 16,453	$ (37,501)	$ (14,646)
Net income (loss) per share - basic	$ 0.41	$ (0.97)	$ (0.41)
Net income (loss) per share - diluted	$ 0.39	$ (0.97)	$ (0.41)
Weighted-average number of shares used in computing net income (loss) per share - basic	39,943	38,814	35,709
Weighted-average number of shares used in computing net income (loss) per share -diluted	42,561	38,814	35,709
Other comprehensive income (loss):
Unrealized gains (losses) on available-for-sale securities, net	$ (12)	$ 153	$ (11)
Comprehensive income (loss)	$ 16,441	$ (37,348)	$ (14,657)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	MLV [Member]	CE Offering [Member]	Common Stock [Member]	Common Stock [Member]MLV [Member]	Common Stock [Member]CE Offering [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]MLV [Member]	Additional Paid-In Capital [Member]CE Offering [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]MLV [Member]	Accumulated Other Comprehensive Income (Loss) [Member]CE Offering [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]MLV [Member]	Accumulated Deficit [Member]CE Offering [Member]
Beginning Balance at Dec. 31, 2013	$ 54,442			$ 31			$ 537,001			$ 7			$ (482,597)
Beginning Balance, shares at Dec. 31, 2013				30,681,624
Issuance of common stock upon exercise of stock options for cash at $6.00 and weighted price of $6.22 and $6.75 per share in 2014, 2015 and 2016 respectively	2			$ 0			2			0			0
Issuance of common stock upon exercise of stock options for cash and weighted price, shares				390
Issuance of common stock pursuant to ESPP at a weighted price of $3.38, $3.24 and $7.08 per share in 2014, 2015 and 2016 respectively	67			$ 0			67			0			0
Issuance of common stock pursuant to ESPP, shares				19,726
Issuance of common stock upon vesting of restricted stock units, net of taxes withheld, value	(96)			$ 0			(96)			0			0
Issuance of common stock upon vesting of restricted stock units, net of taxes withheld, shares				11,704
Issuance of common stock upon exercise of warrants , value	6			$ 1			5			0			0
Issuance of common stock upon exercise of warrants, shares				510,125
Issuance of common stock to collaborative partner for $4.90 per share, net of issuance costs of $8	9,102			$ 2			9,100			0			0
Issuance of common stock to MLV and CE Offering at $6.64-$6.79 and $7.00-$12.68 per share, net of commission and issuance costs of $74 and $205		$ 2,376			$ 0			$ 2,376			$ 0			$ 0
Issuance of common stock to collaborative partner, shares				2,040,816
Issuance of common stock to MLV and CE Offering, shares					364,103
Issuance of common stock pursuant to February 2014 public offerings at $8.00 per share, net of issuance costs of $2,800	37,492			$ 5			37,487			0			0
Stock-based compensation	3,330			0			3,330			0			0
Other comprehensive income (loss)	(11)			0			0			(11)			0
Net loss	(14,646)			0			0			0			(14,646)
Ending Balance at Dec. 31, 2014	92,064			$ 39			589,272			(4)			(497,243)
Ending Balance, shares at Dec. 31, 2014				38,659,738
Issuance of common stock, shares				5,031,250
Issuance of common stock upon exercise of stock options for cash at $6.00 and weighted price of $6.22 and $6.75 per share in 2014, 2015 and 2016 respectively	427			$ 0			427			0			0
Issuance of common stock upon exercise of stock options for cash and weighted price, shares				68,635
Issuance of common stock pursuant to ESPP at a weighted price of $3.38, $3.24 and $7.08 per share in 2014, 2015 and 2016 respectively	69			$ 0			69			0			0
Issuance of common stock pursuant to ESPP, shares				21,167
Issuance of common stock upon vesting of restricted stock units, net of taxes withheld, value	(144)			$ 0			(144)			0			0
Issuance of common stock upon vesting of restricted stock units, net of taxes withheld, shares				23,725
Issuance of common stock upon exercise of warrants , value	0			$ 0			0			0			0
Issuance of common stock upon exercise of warrants, shares				234
Issuance of common stock to MLV and CE Offering at $6.64-$6.79 and $7.00-$12.68 per share, net of commission and issuance costs of $74 and $205			$ 8,673			$ 1			$ 8,672			$ 0			$ 0
Issuance of common stock to MLV and CE Offering, shares						808,193
Issuance of warrants pursuant to the Loan Agreement	282			$ 0			282			0			0
Stock-based compensation	4,567			0			4,567			0			0
Other comprehensive income (loss)	153			0			0			153			0
Net loss	(37,501)			0			0			0			(37,501)
Ending Balance at Dec. 31, 2015	68,590			$ 40			603,145			149			(534,744)
Ending Balance, shares at Dec. 31, 2015				39,581,692
Issuance of common stock upon exercise of stock options for cash at $6.00 and weighted price of $6.22 and $6.75 per share in 2014, 2015 and 2016 respectively	503			$ 0			503			0			0
Issuance of common stock upon exercise of stock options for cash and weighted price, shares				74,556
Issuance of common stock pursuant to ESPP at a weighted price of $3.38, $3.24 and $7.08 per share in 2014, 2015 and 2016 respectively	917			$ 0			917			0			0
Issuance of common stock pursuant to ESPP, shares				129,604
Issuance of common stock upon vesting of restricted stock units, net of taxes withheld, value	(135)			$ 0			(135)			0			0
Issuance of common stock upon vesting of restricted stock units, net of taxes withheld, shares				25,745
Issuance of common stock upon exercise of warrants , value	611			$ 1			610			0			0
Issuance of common stock upon exercise of warrants, shares				834,998
Issuance of warrants pursuant to the Loan Agreement	288			$ 0			288			0			0
Stock-based compensation	7,146			0			7,146			0			0
Other comprehensive income (loss)	(12)			0			0			(12)			0
Net loss	16,453			0			0			0			16,453
Ending Balance at Dec. 31, 2016	$ 94,361			$ 41			$ 612,474			$ 137			$ (518,291)
Ending Balance, shares at Dec. 31, 2016				40,646,595

Consolidated Statements of Sto6

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Issuance of common stock to collaborative partner for cash per share			$ 4.90
Issuance of common stock to collaborative partner issuance costs			$ 8
Issuance of common stock at per share			$ 8
Stock issuance costs			$ 2,800
Issuance of common stock upon exercise of stock options for cash and weighted price, per share	$ 6.75	$ 6.22	$ 6
Issuance of common stock pursuant to ESPP, per share	$ 7.08	3.24	3.38
MLV [Member]
Issuance of common stock to MLV at per share, lower limit			6.64
Issuance of common stock to MLV at per share, upper limit			$ 6.79
Issuance of common stock to MLV, net of commission and issuance costs			$ 74
CE Offering [Member]
Issuance of common stock to CE Offering, at per share, lower limit		7
Issuance of common stock to CE Offering,at per share, upper limit		$ 12.68
Issuance of common stock to CE Offering, net of commission and issuance costs		$ 205

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income (loss)	$ 16,453	$ (37,501)	$ (14,646)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization of property and equipment	741	589	490
Gain on disposal of equipment	(18)	(18)	0
Non-cash interest expense	534	3	0
Stock-based compensation	7,146	4,567	3,330
Gain on sale of investments	0	(3)	(6)
Changes in operating assets and liabilities:
Related party accounts receivable	(12)	46,634	(46,641)
Prepaid and other assets	(707)	(396)	274
Accounts payable	1,698	755	(2,178)
Accrued and other liabilities	8,945	2,995	(2,865)
Deferred revenue	2,202	(12,742)	17,399
Net cash provided by (used in) operating activities	36,982	4,883	(44,843)
Cash flows from investing activities:
Purchases of investments	(145,158)	(115,566)	(107,043)
Proceeds from sales and maturities of investments	94,645	132,190	104,098
Purchases of property and equipment	(1,596)	(562)	(1,104)
Proceeds from sales of property and equipment	33	1	0
Net cash provided by (used in) investing activities	(52,076)	16,063	(4,049)
Cash flows from financing activities:
Proceeds from public offerings of common stock, net of issuance costs	0	8,673	48,971
Proceeds from long term debt, net of debt discount and issuance costs	14,996	14,890	0
Proceeds (payments) from stock based award activities and warrants, net	1,896	352	(22)
Net cash provided by financing activities	16,892	23,915	48,949
Net increase in cash and cash equivalents	1,798	44,861	57
Cash and cash equivalents, beginning of period	65,076	20,215	20,158
Cash and cash equivalents, end of period	$ 66,874	$ 65,076	$ 20,215

Organization and Significant Ac

Organization and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Significant Accounting Policies	Note 1 — Organization and Significant Accounting Policies Organization 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. The Company’s financial statements contemplate the conduct of the Company’s operations in the normal course of business. The Company has incurred an accumulated deficit of $518.3 million since inception and there can be no assurance that the Company will attain profitability. The Company had net income of $16.4 million and net cash provided by operations of $37.0 million for the year ended December 31, 2016. Cash, cash equivalents and investments increased to $163.9 million at December 31, 2016 from $111.6 million at December 31, 2015. The Company anticipates that it will have operating losses and net cash outflows in future periods. The Company is 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 its future plans. The Company’s liquidity will be impaired if sufficient additional capital is not available on terms acceptable to the Company. To date, the Company has funded its operations primarily through sales of its common stock and convertible preferred stock, contract payments under its collaboration agreements, debt financing arrangements, government grants and interest income. Until it achieves profitable operations, the Company intends to continue to fund operations through payments from strategic collaborations, additional sales of equity securities, grants and debt financings. The Company has never generated revenues from commercial sales of its drugs and may not have drugs to market for at least several years, if ever. The Company’s success is dependent on its ability to enter into new strategic collaborations and/or raise additional capital and to successfully develop and market one or more of its drug candidates. As a result, the Company may choose to raise additional capital through equity or debt financings to continue to fund its operations in the future. The Company 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 the Company’s 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 the Company’s future financial results, financial position and cash flows. Based on the current status of its research and development plans, the Company believes that its existing cash, cash equivalents and investments will be sufficient to fund its cash requirements for at least the next 12 months. If, at any time, the Company’s prospects for financing its research and development programs decline, the Company may decide to reduce research and development expenses by delaying, discontinuing or reducing its funding of one or more of its research or development programs. Alternatively, the Company 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. The financial statements do not include any adjustments that might result from the outcome of this uncertainty. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management 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 financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Basis of Presentation The consolidated financial statements include the accounts of Cytokinetics and its wholly owned subsidiary and have been prepared in accordance with U.S. generally accepted accounting principles (“US GAAP”). Intercompany transactions and balances have been eliminated in consolidation. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to concentrations of risk consist principally of cash and cash equivalents, investments, long term debt and accounts receivable. The Company’s cash, cash equivalents and investments are invested in deposits with three major financial institutions in the United States. Deposits in these banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any realized losses on its deposits of cash, cash equivalents or investments. The economic turmoil in the United States in recent years, the extraordinary volatility in the stock markets and other current negative macroeconomic indicators could negatively impact the Company’s ability to raise the funds necessary to support its business and may materially adversely affect its business, operating results and financial condition. The Company performs an ongoing credit evaluation of its strategic partners’ financial conditions and generally does not require collateral to secure accounts receivable from its strategic partners. The Company’s exposure to credit risk associated with non-payment Drug candidates developed by the Company may require approvals or clearances from the U.S. Food and Drug Administration (“FDA”) or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s drug candidates will receive any of the required approvals or clearances. If the Company was to be denied approval or clearance or any such approval or clearance was to be delayed, it would have a material adverse impact on the Company. The Company’s operations and employees are located in the United States. In the year ended December 31, 2016, 27% of the Company’s revenues were received from entities located in the United States and 73% were received from a Japanese entity. In the year ended December 31, 2015, 9% of the Company’s revenues were received from entities located in the United States and 91% were received from a Japanese entity. In the year ended December 31, 2014, 10% of the Company’s revenues were received from entities located in the United States and 90% were received from a Japanese entity. Cash and Cash Equivalents The Company considers all highly liquid investments with a maturity of three months or less at the time of purchase to be cash equivalents. Investments Available-for-sale available-for-sale available-for-sale available-for-sale Other-than-temporary impairment. available-for-sale Fair Value of Financial Instruments The fair value of financial instruments reflects the amounts that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Cash, accounts payable and accrued liabilities are carried at cost, which approximates fair value given their short-term nature. Marketable securities and cash equivalents, are carried at fair value. Property and Equipment, net Property and equipment are stated at cost less accumulated depreciation and are depreciated on a straight-line basis over the estimated useful lives of the related assets, which are generally three years for computer equipment and software, five years for laboratory equipment and office equipment, and seven years for furniture and fixtures. Amortization of leasehold improvements is computed using the straight-line method over the shorter of the remaining lease term or the estimated useful life of the related assets, typically ranging from three to seven years. Upon sale or retirement of assets, the costs and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in operations. Maintenance and repairs are charged to operations as incurred. Impairment of Long-lived Assets In accordance with the accounting guidance for the impairment or disposal of long-lived assets, the Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Under the accounting guidance, an impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is measured as the amount by which the carrying amount of a long-lived asset exceeds its fair value. Revenue Recognition The accounting guidance for revenue recognition requires that the following criteria must be met before revenue can be recognized: (i) persuasive evidence of an arrangement exists; (ii) delivery has occurred or services have been rendered; (iii) the fee is fixed or determinable; and (iv) collectability is reasonably assured. Determination of whether persuasive evidence of an arrangement exists and whether delivery has occurred or services have been rendered are based on management’s judgments regarding the fixed nature of the fee charged for research performed and milestones met, and the collectability of those fees. Should changes in conditions cause management to determine these criteria are not met for certain future transactions, revenue recognized for any reporting period could be adversely affected. Revenue under the Company’s license and collaboration arrangements is recognized based on the performance requirements of the contract. Research and development revenues, which are earned under agreements with third parties for agreed research and development activities, may include non-refundable 605-25, Revenue Recognition — Multiple-Element Arrangements 605-25”) Upfront, non-refundable non-refundable ASC Topic 605-28, Revenue Recognition — Milestone Method 605-28”), Other contingent event-based payments received for which payment is either contingent solely upon the passage of time or the results of a collaborative partner’s performance are not considered milestones under ASC 605-28. The Company accounts for milestone payments under the provisions of ASC 605-28. Research and development revenues and cost reimbursements are based upon negotiated rates for the Company’s full-time employee equivalents (“FTE”) and actual out-of-pocket Funds received from third parties under grant arrangements are recorded as revenue if the Company is deemed to be the principal participant in the grant arrangement as the activities under the grant are part of the Company’s development program. If the Company is not the principal participant, the grant funds are recorded as a reduction to research and development expense. Grant funds received are not refundable and are recognized when the related qualified research and development costs are incurred and when there is reasonable assurance that the funds will be received. Funds received in advance are recorded as deferred revenue. Preclinical Studies and Clinical Trial Accruals A substantial portion of the Company’s preclinical studies and all of the Company’s clinical trials have been performed by third-party contract research organizations (“CROs”) and other vendors. For preclinical studies, the significant factors used in estimating accruals include the percentage of work completed to date and contract milestones achieved. For clinical trial expenses, the significant factors used in estimating accruals include the number of patients enrolled, duration of enrollment and percentage of work completed to date. The Company monitors patient enrollment levels and related activities to the extent practicable through internal reviews, correspondence and status meetings with CROs, and review of contractual terms. The Company’s estimates are dependent on the timeliness and accuracy of data provided by its CROs and other vendors. If the Company has incomplete or inaccurate data, it may under- or overestimate activity levels associated with various studies or trials at a given point in time. In this event, it could record adjustments to research and development expenses in future periods when the actual activity level becomes known. Research and Development Expenditures Research and development costs are charged to operations as incurred. Research and development expenses consist primarily of clinical manufacturing costs, preclinical study expenses, consulting and other third party costs, employee compensation, supplies and materials, allocation of overhead and occupancy costs, facilities costs and depreciation of equipment. Income Taxes The Company accounts 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. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company also follows the accounting guidance that defines the threshold for recognizing the benefits of tax return positions in the financial statements as “more-likely-than-not” Comprehensive Income (Loss) The Company follows the accounting standards for the reporting and presentation of comprehensive income (loss) and its components in a continuous statement of comprehensive income (loss). Comprehensive income (loss) includes all changes in stockholders’ equity during a period from non-owner Segment Reporting The Company has determined that it operates in only one segment — the discovery and development of first-in-class Stock-Based Compensation The Company accounts for stock-based payment awards made to employees and directors, including employee stock options and employee stock purchases by measuring the stock-based compensation cost at the grant date based on the calculated fair value of the award, and recognizing expense on a straight-line basis over the employee’s requisite service period, generally the vesting period of the award. Stock compensation for non-employees The Company reviews the valuation assumptions at each grant date and, as a result, from time to time it will likely change the valuation assumptions it uses to value stock based awards granted in future periods. The assumptions used in calculating the fair value of share-based payment awards represent management’s best estimates at the time, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if conditions change and the management uses different assumptions, the Company’s stock-based compensation expense could be materially different in the future. In addition, the Company is required to estimate the expected forfeiture rate and recognize expense only for those shares expected to vest. If the actual forfeiture rate is materially different from management’s estimate, stock-based compensation expense could be significantly different from what has been recorded in the current period. Recent Accounting Pronouncements In August 2016, the FASB issued ASU 2016-15, ‘Statement of cash flows (Topic 230): Classification of certain cash receipts and cash payments’. ASU 2016-15 2016-15 In June 2016, the FASB issued ASU 2016-13, ‘Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments. ASU 2016-13 2016-13 In March 2016, the FASB issued ASU 2016-09, Stock compensation (Topic 718). ASU 2016-09 . 2016-09 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 right-to-use . 2016-02 In January 2016, the FASB issued ASU 2016-01, Financial instruments (Subtopic 825-10). ASU 2016-01 2016-01 2016-01 In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40): ASU 2014-15 2014-15 2014-12, 2014-12 In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Note 2 — Net Income (Loss) Per Share Basic net income (loss) per share is computed by dividing net income (loss) by the weighted average number of vested common shares outstanding during the period. Diluted net income (loss) per share is computed by giving effect to all potentially dilutive common shares, including outstanding stock options, unvested restricted stock, warrants, convertible preferred stock and shares issuable under the Company’s Employee Stock Purchase Plan (“ESPP”), by applying the treasury stock method. The following is the calculation of basic and diluted net income (loss) per share (in thousands, except per share data): Years Ended December 31, 2016 2015 2014 Net income (loss) $ 16,453 $ (37,501 ) $ (14,646 ) Weighted-average shares used in computing net income (loss) per share — basic 39,943 38,814 35,709 Effect of dilutive securities: Warrants to purchase common stock 2,019 — — Options to purchase common stock 409 — — Restricted stock units 181 — — Shares issuable related to the ESPP 9 — — Dilutive potential common shares 2,618 — — Weighted-average shares used in computing net income (loss) per share — diluted 42,561 38,814 35,709 Net income (loss) per share — basic $ 0.41 $ (0.97 ) $ (0.41 ) Net income (loss) per share — diluted $ 0.39 $ (0.97 ) $ (0.41 ) The following instruments were excluded from the computation of diluted net income (loss) per share for the periods presented because their effect would have been antidilutive (in thousands): December 31, 2016 2015 2014 Options to purchase common stock 3,688 4,835 3,298 Warrants to purchase common stock — 5,641 6,691 Restricted and Performance stock units — 757 63 Shares issuable related to the ESPP — 16 15 Total shares 3,688 11,249 10,067

Supplementary Cash Flow Data

Supplementary Cash Flow Data	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Supplementary Cash Flow Data	Note 3 — Supplementary Cash Flow Data Supplemental cash flow information was as follows (in thousands): Years Ended 2016 2015 2014 Cash paid for interest $ 1,899 $ 94 $ — Cash paid for income taxes 1 1 1 Significant non-cash Debt discount netted against proceeds from long term debt, recorded in equity 288 282 — Interest paid on the long-term debt, at inception 63 41 — Purchases of property and equipment through accounts payable (320 ) (147 ) 170 Purchases of property and equipment through accrued liabilities (747 ) (2 ) 27

Cash Equivalents and Investment

Cash Equivalents and Investments	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Cash Equivalents and Investments	Note 4 — Cash Equivalents and Investments Cash Equivalents and Available for Sale Investments The amortized cost and fair value of cash equivalents and available for sale investments at December 31, 2016 and 2015 were as follows (in thousands): December 31, 2016 Amortized Unrealized Unrealized Fair Maturity Cash equivalents — U. S. Treasury securities and money market funds $ 55,658 $ — $ — $ 55,658 Short-term investments — U.S. Treasury securities $ 89,396 $ 2 $ (23 ) $ 89,375 1/2017 — 12/2017 Long-term investments — Equity and U.S. Treasury securities $ 7,513 $ 176 $ (17 ) $ 7,672 2/2018 — 3/2018 December 31, 2015 Amortized Unrealized Unrealized Fair Maturity Cash equivalents — money market funds $ 63,136 $ — $ — $ 63,136 Short-term investments — U.S. Treasury securities $ 46,395 $ 1 $ (30 ) $ 46,366 2/2016 —8/2016 Long-term investments — equity securities $ — $ 179 $ — $ 179 As of December 31, 2016 and December 31, 2015, the Company’s U.S. Treasury securities classified as short-term investments had unrealized losses of approximately $23,000 and $30,000, respectively. The net unrealized loss at December 31, 2016 and December 31, 2015 was primarily caused by increases in short-term interest rates subsequent to the purchase dates of the related securities. At December 31, 2016 there were no investments that had been in a continuous unrealized loss position for 12 months or longer. The Company collected the contractual cash flows on its U.S. Treasury securities that matured from January 1, 2017 through February 23, 2017 and expects to be able to collect all contractual cash flows on the remaining maturities of its U.S. Treasury securities. Interest income was as follows (in thousands): Years Ended 2016 2015 2014 Interest income $ 449 $ 156 $ 101

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 5 — Fair Value Measurements The Company follows the fair value accounting guidance to value its financial assets and liabilities. Fair value is 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). The Company utilizes market data or assumptions that the Company believes 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. The Company primarily applies the market approach for recurring fair value measurements and endeavors to utilize the best information reasonably available. Accordingly, the Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible, and considers the security issuers’ and the third-party insurers’ credit risk in its assessment of fair value. The Company classifies the determined fair value based on the observability of those inputs. Fair value accounting guidance establishes a fair value 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). The three defined levels of the fair value hierarchy are as follows: 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. Financial assets measured at fair value on a recurring basis as of December 31, 2016 and 2015 are classified in the table below in one of the three categories described above (in thousands): December 31, 2016 Fair Value Measurements Using Assets Level 1 Level 2 Level 3 Assets: Money market funds $ 52,657 $ — $ — $ 52,657 U.S. Treasury securities 99,872 — — 99,872 Equity securities 176 — — 176 Total $ 152,705 $ — $ — $ 152,705 Amounts included in: Cash and cash equivalents $ 55,658 $ — $ — $ 55,658 Short-term investments 89,375 — — 89,375 Long-term investments 7,672 — — 7,672 Total $ 152,705 $ — $ — $ 152,705 December 31, 2015 Fair Value Measurements Using Assets Level 1 Level 2 Level 3 Assets: Money market funds $ 63,136 $ — $ — $ 63,136 U.S. Treasury securities 46,366 — — 46,366 Equity securities 179 — — 179 Total $ 109,681 $ — $ — $ 109,681 Amounts included in: Cash and cash equivalents $ 63,136 $ — $ — $ 63,136 Short-term investments 46,366 — — 46,366 Long-term investments 179 — — 179 Total $ 109,681 $ — $ — $ 109,681 The valuation technique used to measure fair value for the Company’s Level 1 assets is a market approach, using prices and other relevant information generated by market transactions involving identical assets. As of December 31, 2016 and 2015, the Company had no financial assets measured at fair value on a recurring basis using significant Level 2 or Level 3 inputs. The carrying amount of the Company’s accounts receivable and accounts payable approximates fair value due to the short-term nature of these instruments. Long Term Debt: As of December 31, 2016 and December 31, 2015, the fair value of the long-term debt, payable in installments through year ended 2020, approximated its carrying value of $29.9 million and $14.6 million, respectively, because it is carried at a market observable interest rate, which are considered Level 2.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Note 6 — Balance Sheet Components Property and equipment balances were as follows (in thousands): December 31, 2016 2015 Property and equipment, net: Laboratory equipment $ 16,742 $ 15,713 Computer equipment and software 2,699 2,510 Office equipment, furniture and fixtures 856 945 Leasehold improvements 4,458 3,425 Total property and equipment 24,755 22,593 Less: Accumulated depreciation and amortization (21,118 ) (20,842 ) Total property and equipment, net $ 3,637 $ 1,751 Depreciation expense was $0.7 million, $0.6 million and $0.5 million for the years ended December 31, 2016, 2015 and 2014 respectively. Accrued liabilities were as follows (in thousands): December 31, 2016 2015 Accrued liabilities: Clinical and preclinical costs $ 10,092 $ 3,446 Bonus 3,800 2,720 Other payroll related 1,888 1,464 Other accrued expenses 1,595 791 Leasehold improvements 672 — Total accrued liabilities $ 18,047 $ 8,421 Interest receivable on cash equivalents and investments of $0.2 million and $0.2 million is included in prepaid and other current assets at December 31, 2016 and 2015, respectively. The Company sponsors a 401(k) defined contribution plan covering all employees. In 2016, 2015 and 2014, employer contributions to the 401(k) plan were $0.5 million, $0.4 million and $0.3 million, respectively.

Related Parties and Related Par

Related Parties and Related Party Transactions	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Parties and Related Party Transactions	Note 7 — Related Parties and Related Party Transactions Research and Development Arrangements Amgen Inc. (“Amgen”) In December 2006, the Company entered into a collaboration and option agreement with Amgen to discover, develop and commercialize novel small molecule therapeutics, including omecamtiv mecarbil, that activate cardiac muscle contractility for potential applications in the treatment of heart failure (the “Amgen Agreement”). The agreement granted Amgen an option to obtain an exclusive license worldwide, except Japan, to develop and commercialize omecamtiv mecarbil and other drug candidates arising from the collaboration. In May 2009, Amgen exercised its option. As a result, Amgen became responsible for the development and commercialization of omecamtiv mecarbil and related compounds at its expense worldwide (excluding Japan), subject to the Company’s development and commercialization participation rights. Amgen reimburses the Company for certain research and development activities it performs under the collaboration. In June 2013, Cytokinetics and Amgen executed an amendment to the Amgen Agreement to include Japan, resulting in a worldwide collaboration (the “Amgen Agreement Amendment”). Under the terms of the Amgen Agreement Amendment, the Company received a non-refundable pre-commercialization In conjunction with the Amgen Agreement Amendment, the Company also entered into a common stock purchase agreement which provided for the sale of 1,404,100 shares of its common stock to Amgen at a price per share of $7.12 and an aggregate purchase price of $10.0 million, which was received in June 2013. The Company determined the fair value of the stock issued to Amgen to be $7.5 million. The excess of cash received over fair value of $2.5 million was initially deferred and allocated between the license and services based on their relative selling prices using best estimate of selling price. The allocated consideration was recognized as revenue as revenue criteria were satisfied, or as services were performed over approximately 12 months. Pursuant to this agreement, Amgen agreed to certain trading and other restrictions with respect to the Company’s common stock. The Company determined that the license to the Japan territory granted under the Amgen Agreement Amendment was a separate, non-contingent know-how In October 2013, the Company determined that the revenue recognition requirements under ASC 605-10 Amgen and the Company continued the research program in 2016. Under the amended Amgen Agreement, the Company is entitled to receive reimbursements of internal costs of certain full-time employee equivalents during 2016, as well as potential additional milestone payments related to the research activities. Under the Amgen Agreement, as amended, the Company is eligible to receive over $300.0 million in additional development milestone payments which are based on various clinical milestones, including the initiation of certain clinical studies, the submission of a drug candidate to certain regulatory authorities for marketing approval and the receipt of such approvals. Additionally, the Company is 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, it is not possible to estimate if and when these milestone payments would become due. The achievement of each of these milestones is dependent solely upon the results of Amgen’s development and commercialization activities. During the year ended December 31, 2016, the Company recognized $26.7 million in development milestone payments related to the start of GALACTIC-HF, The Amgen Agreement also provides for the Company to receive increased royalties by co-funding co-fund co-promote co-funded In July 2013, Amgen announced that it had granted an option to commercialize omecamtiv mecarbil in Europe to Servier, with the Company’s consent, pursuant to an Option, License and Collaboration Agreement (the “Servier Agreement”). In August 2016, the Company entered into a Letter Agreement with Amgen and Servier (the “Letter Agreement”), which (i) expands the territory of the sublicense to Servier to include specified countries in the Commonwealth of Independent States (“CIS”) and (ii) provides that, if Amgen’s rights under the Amgen Agreement, as amended, are terminated with respect to the territory of such sublicense, the sublicensed rights previously granted by Amgen to Servier under the Servier Agreement will remain in effect and become a direct license or sublicense of such rights by us to Servier, on substantially the same terms as set forth in the Servier Agreement, including but not limited to Servier’s payment of its share of agreed development costs and future milestone and royalty payments to us. The Letter Agreement does not otherwise modify our rights and obligations under the Amgen Agreement, as amended, or create any additional financial obligations of the Company, unless we otherwise agree in writing. In September 2016, Amgen and Servier announced Servier’s decision to exercise its option to commercialize omecamtiv mecarbil in Europe as well as the CIS, including Russia. The option and related commercialization sublicense to Servier is subject to the terms and conditions of the Amgen Agreement. Amgen remains responsible for the performance of its obligations under the Amgen Agreement relating to Europe and the CIS, including the payment of milestones and royalties relating to the development and commercialization of omecamtiv mecarbil in Europe and the CIS. In December 2016, the Company provided notice of its exercise of its option under the Amgen Agreement to co-invest co-invest co-investment co-invest co-invest Pursuant to the Amgen Agreement, the Company has recognized research and development revenue from Amgen for reimbursements of internal costs of certain full-time employee equivalents, supporting a collaborative research program directed to the discovery of next-generation cardiac sarcomere activator compounds and of other costs related to that research program. These reimbursements were recorded as research and development revenues from related parties. During the years ended December 31, 2016, 2015 and 2014, the Company recorded net research and development revenue from Amgen of $27.9 million, $2.5 million and $4.5 million, respectively, under the Amgen Agreement. There were no accounts receivable due from Amgen during the years ended December 31, 2016 and 2015. Revenue from Amgen was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Research and development revenues from related parties, net: Reimbursement of internal costs $ 2,466 $ 2,460 $ 4,260 Research and development milestone fees 26,666 — — Co-invest (1,250 ) — — Allocated consideration — 21 278 Total Research and development revenues from related parties, net 27,882 2,481 4,538 Total net revenues from Amgen $ 27,882 $ 2,481 $ 4,538 There were no accounts receivable due from Amgen at December 31, 2016 and 2015. Astellas Pharma Inc. (“Astellas”) Original Astellas Agreement (Non-neuromuscular In June 2013, the Company entered into a license and collaboration agreement with Astellas (the “Original Astellas Agreement”). The primary objective of the collaboration with Astellas is to advance novel therapies for diseases and medical conditions associated with muscle weakness. Under the Original Astellas Agreement, the Company granted Astellas an exclusive license to co-develop CK-2127107, non-neuromuscular CK-2127107 CK-2127107. In July 2013, the Company received an upfront, non-refundable At the inception of the Original Astellas Agreement, the Company deferred revenue related to the Original Astellas Agreement in accordance with ASC 605-25. non-refundable The Company determined that the license and the research and development services are a single unit of accounting as the license was determined to not have stand-alone value. Accordingly, the Company is recognizing this revenue using the proportional performance model over the initial research term of the Original Astellas Agreement. During the years ended December 31, 2016, 2015 and 2014, the Company recorded zero, $2.3 million and $9.8 million, respectively, in license revenue based on the proportional performance model under the Original Astellas Agreement. No license revenue remains deferred under the Original Astellas Agreement as of December 31, 2016. Pursuant to the Original Astellas Agreement, the Company 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. During the years ended December 31, 2016, 2015 and 2014, the Company recorded research and development revenue from Astellas of zero, $3.5 million and $15.4 million, respectively, under the Original Astellas Agreement. 2014 Astellas Agreement (Expansion to include neuromuscular indications) In December 2014, the Company entered into an amended and restated license and collaboration agreement with Astellas (the “2014 Astellas Agreement”). This agreement superseded the Original Astellas Agreement. The 2014 Astellas Agreement expanded the objective of the collaboration of advancing novel therapies for diseases and medical conditions associated with muscle weakness to include spinal muscular atrophy (“SMA”) and potentially other neuromuscular indications for CK-2127107 non-neuromuscular Under the 2014 Astellas Agreement, the Company received a non-refundable CK-2127107 CK-2127107 The Company determined that the license and the research and development services relating to the 2014 Astellas Agreement are a single unit of accounting as the license was determined to not have stand-alone value. Accordingly, the Company is recognizing this revenue over the research term of the 2014 Astellas Agreement using the proportional performance model. During the years ended December 31, 2016 and 2015, the Company recorded $12.1 million and $11.6 million, respectively, in license revenue based on the proportional performance model under the 2014 Astellas Agreement. No such revenues were recognized during the year ended December 31, 2014. As of December 31, 2016, $7.2 million license revenue remains deferred under the 2014 Astellas Agreement. Pursuant to the 2014 Astellas Agreement, the Company 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. The Company was eligible to potentially receive over $20.0 million in reimbursement of sponsored research and development activities during the two years of the collaboration following the execution of the 2014 Astellas Agreement. During the years ended December 31, 2016 and 2015, the Company recorded research and development revenue from Astellas of $13.0 million and $8.7 million, respectively, under the 2014 Astellas Agreement. No such revenues were recognized during the year ended December 31, 2014. In conjunction with the 2014 Astellas Agreement, the Company also entered into a common stock purchase agreement which provided for the sale of 2,040,816 shares of its common stock to Astellas at a price per share of $4.90 and an aggregate purchase price of $10.0 million which was received in December 2014. Pursuant to this agreement, Astellas agreed to certain trading and other restrictions with respect to the Company’s common stock. The Company determined the fair value of the stock issued to Astellas to be $9.1 million. The excess of cash received over fair value of $0.9 million was deferred along with the license and research and development services. Allocated consideration will be recognized as revenue for the single unit of accounting above, as services are performed following the proportional performance model over the research term of the 2014 Astellas Agreement. Following the common stock purchase, Astellas was determined to be a related party. As such, all revenue earned following the common stock purchase is classified as related party revenue. 2016 Astellas Amendment (Inclusion of ALS as an Added Indication and Option on Tirasemtiv) In 2016, Cytokinetics and Astellas further amended the collaboration agreement to expand our collaboration to include the development of CK-2127107 Under the 2016 Astellas Amendment, the Company granted Astellas the Option on Tirasemtiv. If Astellas exercises the option, Astellas will receive exclusive worldwide commercialization rights outside of the Company’s commercialization territory of North America, Europe and other select countries. Tirasemtiv is the Company’s fast skeletal troponin activator being evaluated in the ongoing Phase 3 clinical trial, VITALITY-ALS, In addition, the 2016 Astellas Amendment expands the Company’s collaboration with Astellas to include the development of CK-2127107, Astellas’ Option on Tirasemtiv In connection with the execution of the 2016 Astellas Amendment, the Company received a $15.0 million non-refundable VITALITY-ALS If Astellas exercises its option for a global collaboration for the development and commercialization of tirasemtiv, the Company will receive an option exercise payment ranging from $25.0 million (if exercise occurs following receipt of data from the VITALITY-ALS (VIGOR-ALS). VITALITY-ALS, If Astellas exercises the option for tirasemtiv, 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, the Company may receive milestone payments up to $100.0 million for the initial indication and up to $50.0 million for each subsequent indication. If tirasemtiv is commercialized, Astellas will pay the Company royalties (at rates ranging from the mid-teens mid-teens) The Company concluded that the option to obtain the License on Tirasemtiv is a substantive option, and is therefore not considered a deliverable at the execution of the 2016 Astellas Amendment. The Company determined that the Tirasemtiv License Agreement is contingent upon the exercise of the Option on Tirasemtiv, and is therefore not effective during the periods presented, since the option has not been exercised as of the latest balance sheet date. In addition, the Company did evaluate the consideration set to be received for the License on Tirasemtiv in relation to the fair value of the License on tirasemtiv, and determined that it was not being provided at a significant incremental discount. The Company further determined that the Option Fee of $15.0 million was deemed to be a prepayment towards the License on tirasemtiv, and therefore deferred revenue recognition either until the option is exercised, or until the option expires unexercised. If the Option on Tirasemtiv expires unexercised, the $15.0 million received would be added to the 2016 Astellas Amendment consideration, to be allocated to the units of accounting. The Option on Tirasemtiv expires, if not exercised by Astellas, following the receipt of the approval letter for tirasemtiv from the FDA. Prior to Astellas’ exercise of the option, the Company will continue the development of tirasemtiv, including the VITALITY-ALS Addition of ALS as an Added Indication (CK-2127107 In connection with the execution of the 2016 Astellas Amendment, the Company received a non-refundable CK-2127107 The Company and Astellas are collaborating to develop CK-2127107 in ALS. Astellas is primarily responsible for the development of CK-2127107 in ALS, but the Company will conduct the Phase 2 clinical trial of CK-2127107 in ALS and will share in the operational responsibility for later clinical trials. Subject to specified guiding principles, decision making will be by consensus, subject to escalation and, if necessary, Astellas’ final decision making authority on the development (including regulatory affairs), manufacturing, medical affairs and commercialization of CK-2127107 and other fast skeletal regulatory activators in ALS. The Company and Astellas will share equally the costs of developing CK-2127107 CK-2127107 co-funding co-fund CK-2127107 Pursuant to the 2016 Astellas Amendment, the Company and Astellas will collaborate to develop CK-2127107 CK-2127107 CK-2127107 CK-2127107 The Company determined that the deliverables under the 2016 Astellas Amendment included (1) the ALS License, (2) CK-2127107 The Company considered the 2016 Astellas Amendment to be a modification of the 2014 Astellas Agreement. The remaining deliverables under the 2014 Astellas Agreement are: (1) the SMA license; (2) Research Services in connection with the Research Plan (through 2016); and (3) SMA Development Services in connection with the Development Plan. The Company evaluated the components and consideration of the 2016 Astellas Amendment against other Phase 2 collaboration arrangements, and determined that the new 2016 deliverables had standalone value and are delivered at fair value. Therefore no reallocation of consideration to the 2014 deliverables was performed. The Company concluded that there are two units of accounting; the ALS License, and the Additional Research Services and ALS Development Services (“Research and ALS Development Services”). The Company also determined that the ALS License has standalone value since (1) Astellas received a worldwide license for ALS, to perform further research in the field of ALS, to develop and use CK-2127107 CK-2127107 CK-2127107 CK-2127107 Arrangement Consideration under the 2016 Astellas Amendment related to CK-2127107 Arrangement Amendment Fee $ 35.0 Accelerated milestone payment 15.0 Total Upfront Consideration 50.0 Additional Research Services 5.1 ALS Development Services 39.1 Total Committed Consideration 44.2 Total Consideration $ 94.2 The Company allocated the $50.0 million in upfront consideration along with the $44.2 million in then committed research and development consideration, among the two units of accounting, on a relative fair value basis, using the best estimated selling price (“BESP”). The BESP of the ALS License was determined using a discounted cash flow, risk adjusted for probability of success; while the BESP of the research and development services were determined using estimated research and development cost, included in the research and development programs approved by Astellas. Based on this allocation of consideration, the Company stands to recognize $74.9 million in license revenue and $19.3 in research and development revenue, under the 2016 Astellas Amendment. Since the upfront consideration of $50.0 million is less than the allocated consideration of the ALS License, the Company recognized $50.0 million in license revenue on the Amendment Effective Date, in September 2016, and record the remaining $24.9 million as an allocation from research and development services, when those services are performed. Allocation of arrangement consideration, and revenue recognition (in millions): Allocated Upfront Revenue Units of Accounting: ALS License $ 74.9 $ 50.0 $ 24.9 Research and ALS Development Services 19.3 — 19.3 Total consideration $ 94.2 $ 50.0 $ 44.2 During the year ended December 31, 2016, the Company recorded $50.1 million in license revenue under the 2016 Astellas Amendment. The Company will recognize the research and development services using the proportional performance model over the initial development term, through the completion of the ALS Development Services. Pursuant to the 2016 Astellas Amendment, the Company receives payment for 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. During the year ended December 31, 2016, the Company recorded $0.1 million research and development revenue from Astellas, under the 2016 Astellas Amendment. The Company believes that each of the milestones related to research under the Current Astellas Agreement is substantive and can only be achieved with the Company’s past and current performance and each milestone will result in additional payments to the Company. During the year ended December 31, 2016, the Company recorded $2.0 million in milestone revenue for research under this agreement, related to the initiation of IND-enabling The achievement of each of the late stage development milestones and the commercialization milestones are dependent solely upon the results of Astellas’ development activities and therefore these milestones were not deemed to be substantive. Under the Current Astellas Agreement, additional research and early and late state development milestone payments which are based on various research and clinical milestones, including the initiation of certain clinical studies, the submission for approval of a drug candidate to certain regulatory authorities for marketing approval and the commercial launch of collaboration products could total over $600.0 million, including up to $95.0 million relating to CK-2127107 non-neuromuscular CK-2127107 In the event Astellas commercializes any collaboration products, the Company will receive royalties on sales of such collaboration products, including royalties ranging from the high single digits to the high teens on sales of products containing CK-2127107. co-fund CK-2127107 co-promote co-promote co-promotion Research and development revenue from Astellas was as follows (in thousands): Year Ended Year Ended Year Ended License Revenues from Related Parties $ 62,171 $ 13,918 $ 9,835 Research and development revenues with related parties: Reimbursement of internal costs 6,111 6,210 — Reimbursement of other costs 6,999 5,974 — Research and development milestone fees 2,000 — 15,000 Total research and development revenue with related parties from Astellas $ 15,110 $ 12,184 $ 15,000 Research and development revenues: Reimbursement of internal costs — — 8,939 Reimbursement of other costs — — 6,452 Research and development milestone fees — — 2,000 Total research and development revenue from Astellas — — 17,391 Total Revenue from Astellas $ 77,281 $ 26,102 $ 42,226 At December 31, 2016 and December 31, 2015, the Company had $23.1 million and $20.4 million, respectively, of deferred revenue under the Current Astellas Agreement, reflecting the unrecognized portion of the license revenue, option fee and payment of expenses. There were no accounts receivable due from Astellas at December 31, 2016 and 2015.

Other Research and Development

Other Research and Development Revenue Arrangements Grants	12 Months Ended
	Dec. 31, 2016
Research and Development [Abstract]
Other Research and Development Revenue Arrangements Grants	Note 8 — Other Research and Development Revenue Arrangements Grants In July 2015, The ALS Association (the “ALSA Grant”) awarded to the Company a $1.5 million grant to support the conduct of VITALITY-ALS VITALITY-ALS Total grant revenues were as follows (in thousands): Years Ended 2016 2015 2014 ALSA grant revenue $ 1,084 $ 75 $ — Other grant revenue — — 75 Total grant revenue $ 1,084 $ 75 $ 75 MyoKardia, Inc. In August 2012, the Company entered into a collaboration agreement with MyoKardia, Inc. Under an agreed research plan, scientists from MyoKardia and our FTEs conduct research focused on small molecule therapeutics that inhibit cardiac sarcomere proteins. The Company provided to MyoKardia access to certain research facilities, and continues to provide FTEs and other resources at agreed reimbursement rates that approximate our costs. The research plan terminated as planned in August 2013. The Company may receive development milestone payments which are based on various clinical milestones. Research and development revenue from MyoKardia was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Research and development milestone fees $ 150 $ — $ 100 Research and development revenue from Myokardia $ 150 $ — $ 100

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Long-Term Debt	Note 9 — Long-Term Debt Long-term debt and unamortized debt discount balances are as follows (in thousands): December 31, 2016 2015 Notes payable, gross $ 30,000 $ 15,000 Less: Unamortized debt discount (472 ) (389 ) Accretion of final exit fee 353 28 Carrying value of notes payable 29,881 14,639 Less: Current portion of long-term debt (2,500 ) — Long-term debt $ 27,381 $ 14,639 In October 2015, the Company entered into a loan and security agreement (the “Loan Agreement”) with Oxford Finance LLC (“Oxford,”) as the collateral agent and a lender, and Silicon Valley Bank (“SVB,”) as a lender (Oxford and SVB collectively the “Lenders”) to fund its working capital and other general corporate needs. The Loan Agreement provided for (1) term loans of up to $40.0 million in aggregate, (2) warrants to purchase 65,189 shares of the Company’s common stock at an exercise price of $6.90 per share under the first term loan, and (3) additional warrants to purchase shares of the Company’s common stock to be based on the amount of the additional term loans and a price per share determined on the day of funding in accordance with the Grant Agreement, which is also the exercise price per share for the warrants. The Company drew down $15.0 million in funds under the Loan Agreement in October 2015 at the time of the first draw down, and at that time, could at its sole discretion draw down an additional $25.0 million under the Loan Agreement in two term loans, provided certain specified conditions stipulated in the Loan Agreement are met preceding those draws. During February 2016, the Company drew down an additional $15.0 million in funds under the Loan Agreement and issued warrants to purchase 68,285 shares of the Company’s common stock at an exercise price of $6.59 per share under the second term loan. As of December 31, 2016, there were 133,474 warrants outstanding and exercisable and are classified under stockholder’s equity. In January 2017, the Company issued 33,368 shares of common stock related to the cashless exercise of 16,126 warrants issued under the Loan Agreement. As of December 31, 2016 the Company received $29.8 million from this loan and security agreement, net of issuance cost. The Company can at its sole discretion draw down an additional $10.0 million under the Loan Agreement from the Lenders, at any time prior to March 31, 2017, subject to the Company’s satisfaction of specified conditions precedent related to the earlier of (i) the occurrence of an equity event as described in the Loan Agreement, or (ii) specified results from the Company’s VITALITY-ALS In accordance with the accounting guidance, the Company allocated a portion of the gross proceeds from each draw down under the Loan Agreement to the underlying warrants, using the relative fair value method. This resulted in the allocation of $0.6 million of the draw down proceeds to the warrants, which was accounted for as debt discount. Debt discount is being amortized over the term of the debt, and recorded in interest expense in the statement of operations. The fair value of the warrants was determined using the Black-Scholes pricing model and are classified as equity. The Loan Agreement contains customary representations and warranties and customary affirmative and negative covenants applicable to the Company and its subsidiaries, including, among other things, restrictions on dispositions, changes in business, management, ownership or business locations, mergers or acquisitions, indebtedness, encumbrances, distributions, investments, transactions with affiliates and subordinated debt. The Agreement also includes customary events of default, including but not limited to the nonpayment of principal or interest, violations of covenants, material adverse changes, attachment, levy, restraint on business, cross-defaults on material indebtedness, bankruptcy, material judgments, misrepresentations, subordinated debt, governmental approvals, lien priority and delisting. Upon an event of default, the Lenders may, among other things, accelerate the loans and foreclose on the collateral. The Company’s obligations under the Agreement are secured by substantially all of the Company’s current and future assets, other than its intellectual property. The Company recorded interest expense related to the long-term debt of $2.7 million and $0.3 million for the years ended December 31, 2016 and 2015, respectively. Included in interest expense for this period was interest on principal, amortization of the debt discount and debt issuance costs, and the accretion of the final exit fee. For the years ended December 31, 2016 and 2015, the effective interest rate on the amounts borrowed under the Agreement, including the amortization of the debt discount and issuance cost, and the accretion of the final payment, was 9.3%. Future minimum payments under the Loan, as of December 31, 2016 are as follows (in thousands): 2017 $ 4,768 2018 11,743 2019 10,982 2020 8,938 Total minimum payments 36,431 Less: Interest and final payment (6,431 ) Notes payable, gross $ 30,000

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 10 — Commitments and Contingencies Commitments Operating Lease The Company leases office space and equipment under a non-cancelable Rent expense was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Rent expense $ 3,448 $ 3,297 $ 3,338 As of December 31, 2016, future minimum lease payments under noncancelable operating leases were as follows (in thousands): 2017 $ 3,703 2018 1,860 2019 — 2020 — 2021 — Thereafter — Total $ 5,563 Co-investment In December 2016, the Company has agreed to exercise its option to co-invest co-investment As of December 31, 2016, future minimum payments due to Amgen were as follows (in thousands): 2017 $ 5,000 2018 3,750 Total $ 8,750 In February 2017, the Company provided notice of its further exercise of its co-invest co-invest Contingencies In the ordinary course of business, the Company 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 the Company’s breach of such agreements, services to be provided by or on behalf of the Company, or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with its directors and certain of its officers and employees that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. The Company maintains director and officer insurance, which may cover certain liabilities arising from its obligation to indemnify its directors and certain of its officers and employees, and former officers and directors in certain circumstances. The Company maintains product liability insurance and comprehensive general liability insurance, which may cover certain liabilities arising from its 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. Management is not currently aware of any matters that could have a material adverse effect on the financial position, results of operations or cash flows of the Company. In December 2014, the Company filed a lawsuit alleging fraudulent inducement, breach of contract and negligence on the part of a contract research organization for BENEFIT-ALS.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Stockholders' Equity	Note 11 — Stockholders’ Equity Preferred Stock As of December 31, 2016 and 2015, respectively, there were 10,000,000 shares of preferred stock authorized and no shares outstanding. Common Stock As of December 31, 2016 and 2015, respectively, there were 163,000,000 shares and 81,500,000 shares of common stock authorized and 40,646,595 and 39,581,692 shares outstanding. Accumulated Other Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income (loss). Other comprehensive income (loss) is comprised of unrealized holding gains and losses on the Company’s available-for-sale In 2016 and 2015, the Company recorded insignificant amounts of unrealized gains (losses) in available-for-sale Common Stock Outstanding In June 2011, the Company entered into an At-The-Market On June 25, 2012, pursuant to the June 2012 Public Offerings, in aggregate the Company issued to various investors (i) 9,320,176 shares of common stock for a purchase price of $4.56 per share, (ii) 23,026 shares of the Series B Preferred Stock for a purchase price of $760.00 per share, and (iii) warrants to purchase 7,894,704 shares of the Company’s common stock at an exercise price of $5.28 per share, for aggregate gross proceeds of approximately $60.0 million. After issuance costs of approximately $4.0 million, the net proceeds from the June 2012 Public Offerings were approximately $56.0 million. Through December 31, 2016, the Company issued 4,104.966 shares of common stock related to exercises of warrants in accordance with the June 2012 Public Offerings. In conjunction with the Amgen Agreement Amendment (see Note 7), in June 2013, Amgen purchased 1,404,100 shares of the Company’s common stock at a price per share of $7.12 and an aggregate purchase price of $10.0 million, which was received in June 2013. Under the terms of this agreement, Amgen agreed to certain trading and other restrictions with respect to the Company’s common stock. The Company determined the fair value of the stock issued to Amgen to be $7.5 million. The excess of cash received over fair value of $2.5 million was deferred and is being allocated between the license and services based on their relative selling prices using best estimate of selling price. In February 2014, the Company closed an underwritten public offering for the issuance and sale of 5,031,250 shares of its common stock. The gross public offering proceeds were approximately $40.3 million. The net proceeds from the sale of the shares were approximately $37.5 million, after deducting the underwriting discount and offering expenses. In December 2014, the Company also entered into a common stock purchase agreement which provided for the sale of 2,040,816 shares of its common stock to Astellas at a price per share of $4.90 and an aggregate purchase price of $10.0 million, which was received in December 2014. On September 4, 2015, the Company entered into an Committed Equity Offering (an “CE Offering”) that is an at-the-market S-3, Sales of the Company’s common stock, through Cantor Fitzgerald, will be made on The NASDAQ Global Market by means of ordinary brokers’ transactions at market prices or as otherwise agreed to by the Company and Cantor Fitzgerald. Subject to the terms and conditions of the Cantor Fitzgerald Agreement, Cantor Fitzgerald will use commercially reasonable efforts to sell the Company’s common stock from time to time, based upon our instructions (including any price, time or size limits or other customary parameters or conditions we may impose). The Company is not obligated to make any sales of common stock under the Cantor Fitzgerald Agreement. The offering of shares of common stock pursuant to the Cantor Fitzgerald Agreement will terminate upon the earlier of (1) the sale of all common stock subject to the Cantor Fitzgerald Agreement or (2) termination of the Cantor Fitzgerald Agreement. The Cantor Fitzgerald Agreement may be terminated by Cantor Fitzgerald at any time upon ten days’ notice to the Company or may be terminated by the Company at any time upon five day’ s notice to Cantor Fitzgerald, or by Cantor Fitzgerald at any time in certain circumstances, including the occurrence of a material adverse change in the Company’s business. The Company will pay Cantor Fitzgerald a commission rate equal to 3.0% of the gross proceeds of the sales price per share of any common stock sold through Cantor Fitzgerald under the Cantor Fitzgerald Agreement. The Company has also provided Cantor Fitzgerald with customary indemnification and contribution rights. As of December 31, 2016, 808,193 shares have been issued through Cantor Fitzgerald under the Cantor Fitzgerald Agreement for total net proceeds of approximately $8.9 million. Through February 23, 2017, the Company issued and sold 993,408 shares for total net proceeds of approximately $11.0 million and $28.7 million remains available to us under the September 2015 Registration Statement. Warrants As of December 31, 2016, the Company had warrants outstanding to purchase 4.2 million shares of the Company’s common stock. In June 2012, warrants were issued pursuant to the June 2012 underwriting agreements the Company entered into in connection with two separate, concurrent offerings for our securities (the “June 2012 Public Offerings”). In accordance with the accounting guidance for valuing stock and warrants when stock is issued in conjunction with other securities, and the stock and other securities are to be accounted for as equity, the Company allocated the gross purchase proceeds using the relative fair value method. For accounting purposes, the June 2012 Public Offerings were considered to be one transaction. The fair value of the common stock issued in the June 2012 Public Offerings was calculated based on the closing price of the stock on the commitment date as quoted on The NASDAQ Global Market. In October 2015, warrants to purchase 65,189 shares of the Company’s common stock at an exercise price of $6.90 per share were issued in accordance with the Loan Agreement. Refer to Note 9 “Long-Term Debt”, for further details regarding the Loan Agreement. In February 2016, warrants to purchase 68,285 shares of the Company’s common stock at an exercise price of $6.59 per share were issued in accordance with the Loan Agreement. The Company valued the warrants as of the date of issuance at $288,000 using the Black-Scholes option pricing model and the following assumptions: a contractual term of five years, a risk-free interest rate of 1.7%, volatility of 75%, and the fair value of the Company’s common stock of $7.00. In August 2016, warrants to purchase 104,533 shares of the Company’s common stock at an exercise price of $5.28 per share were cash exercised in accordance with the June 2012 public offerings underwriting agreements. In September 2016, the Company issued 690,580 shares of common stock related to cashless exercises of warrants in accordance with the June 2012 public offerings. In December 2016, the Company issued 28,569 shares of common stock related to cashless exercises of warrants in accordance with the June 2012 public offerings. Outstanding warrants as of December 31, 2016 were as follows: Number Exercise Expiration Issued 6/25/2012 4,104,966 $ 5.28 06/25/17 Issued 10/19/2015 65,189 $ 6.90 10/19/20 Issued 02/10/2016 68,285 $ 6.59 02/10/21 Equity Incentive Plan Total employee stock-based compensation expenses were $7.1 million, $4.6 million and $3.3 million for the years ended December 31, 2016, 2015 and 2014, respectively. Stock Option Plans 2004 Plan In January 2004, the Board of Directors adopted the 2004 Equity Incentive Plan (the “2004 Plan”), which was approved by the stockholders in February 2004. The 2004 Plan provides for the granting of incentive stock options, nonstatutory stock options, restricted stock, stock appreciation rights, stock performance units and stock performance shares to employees, directors and consultants. Under the 2004 Plan, options may be granted at prices not lower than 100% of the fair market value of the common stock on the date of grant for nonstatutory stock options and incentive stock options and may be granted for terms of up to ten years from the date of grant. Options granted to new employees generally vest 25% after one year and monthly thereafter over a period of four years. Options granted to existing employees generally vest monthly over a period of four years. At the May 2013 Annual Meeting of Stockholders, the number of shares of common stock authorized for issuance under the 2004 Plan was increased by 2,000,000. At the May 2015 Annual Meeting of Stockholders, the number of shares of common stock authorized for issuance under the 2004 Plan was increased by 3,130,000. As of December 31, 2016, there were 1,588,300 shares of common stock reserved for issuance under the 2004 Plan. Stock Options Activity under the Equity Incentive Plan was as follows: Shares Stock Options Weighted Weighted Aggregate Balance at December 31, 2013 2,161,829 2,449,365 $ 15.15 Options granted (944,831 ) 944,831 8.80 Restricted stock units granted (43,500 ) — — Options exercised — (390 ) 6.00 Options forfeited/expired 95,980 (95,980 ) 39.74 Restricted stock units forfeited 1,000 — — Balance at December 31, 2014 1,270,478 3,297,826 $ 12.62 Increase in authorized shares 3,130,000 — — Options granted (1,175,730 ) 1,175,730 7.62 Restricted stock units granted (739,000 ) — — Options exercised — (68,635 ) 6.22 Options forfeited/expired 326,762 (326,762 ) 16.83 Restricted stock units forfeited 3,500 — — Balance at December 31, 2015 2,816,010 4,078,159 $ 10.94 Options granted (1,446,675 ) 1,446,675 7.10 Restricted stock units granted (47,000 ) — — Options exercised — (74,556 ) 6.75 Options forfeited/expired 257,465 (257,465 ) 24.25 Restricted stock units forfeited 8,500 — — Balance at December 31, 2016 1,588,300 5,192,813 $ 9.27 6.83 $ 21,294 Exercisable at December 31, 2016 3,364,286 $ 10.24 5.83 $ 12,771 Vested and expected to vest as of December 31, 2016 5,147,387 $ 9.29 6.81 $ 21,075 Total intrinsic value of stock options exercised was $202,000, $94,000, and $1,000 during the years ended December 31, 2016, 2015 and 2014, respectively. The intrinsic value is calculated as the difference between the market value at the date of exercise and the exercise price of the shares. The market value as of December 31, 2016 was $12.15 per share as reported by NASDAQ. The weighted average grant date fair value of stock options granted was $4.77, $5.35 and $6.01 per share during the years ended December 31, 2016, 2015 and 2014, respectively. The number of option shares vested was 970,241, 713,078 and 601,647 in 2016, 2015 and 2014, respectively. The grant date fair value of option shares vested was $4.9 million, $3.6 million and $3.0 million in 2016, 2015 and 2014, respectively. Restricted Stock Units Restricted stock unit activity was as follows: Number of Weighted Restricted stock units outstanding at December 31, 2013 41,663 $ 6.00 Restricted stock units granted 43,500 9.65 Restricted stock units vested (20,833 ) 6.00 Restricted stock units forfeited (1,000 ) 6.00 Unvested restricted stock units outstanding at December 31, 2014 63,330 8.51 Restricted stock units granted 54,000 7.96 Restricted stock units vested (42,078 ) 7.82 Restricted stock units forfeited (3,500 ) 8.68 Unvested restricted stock units outstanding at December 31, 2015 71,752 8.49 Restricted stock units granted 47,000 6.67 Restricted stock units vested (45,750 ) 8.69 Restricted stock units forfeited (8,500 ) 7.20 Unvested restricted stock units outstanding at December 31, 2016 64,502 7.19 Restricted stock activities were limited to non-executive For the years ended December 31, 2016, 2015 and 2014, the total fair value of restricted stock units vested was $0.4 million, $0.3 million and $0.1 million, respectively. The Company measures compensation expense for restricted stock units at fair value on the grant date and recognizes the expense over the expected vesting period. The fair value for restricted stock units is based on the closing price of the Company’s common stock on the grant date. Unvested restricted stock units are subject to repurchase at no cost to the Company. Restricted Stock Units that Contain Performance Conditions Performance stock unit activity was as follows: Number of Weighted Performance stock units outstanding at December 31, 2014 — $ — Restricted stock units granted 685,000 7.00 Restricted stock units vested — — Restricted stock units forfeited — — Unvested restricted stock units outstanding at December 31, 2015 685,000 7.00 Restricted stock units granted — — Restricted stock units vested — — Restricted stock units forfeited — — Unvested restricted stock units outstanding at December 31, 2016 685,000 $ 7.00 During the year ended December 31, 2015, the Company granted 685,000 performance stock unit awards with a grant date fair value of $7.00 per share that contain performance conditions. As of December 31, 2016, all these performance stock units remain unvested. No performance stock units vested during the years ended December 31, 2016, 2015 and 2014 respectively. The Company measures compensation expense for performance stock units at fair value on the grant date and recognizes the expense over the expected vesting period once it is probable that the performance conditions will be achieved. The fair value for performance stock units is based on the closing price of the Company’s common stock on the grant date. Unvested performance stock awards are subject to repurchase at no cost to the Company. Stock-Based Compensation The Company applies the accounting guidance for stock compensation, which establishes accounting for share-based payment awards made to employees, non-employees The following table summarizes stock-based compensation related to stock options, restricted stock awards, restricted stock unit, and employee stock purchases (in thousands): Years Ended December 31, 2016 2015 2014 Research and development $ 4,252 $ 1,828 $ 1,361 General and administrative 2,894 2,739 1,969 Stock-based compensation included in operating expenses $ 7,146 $ 4,567 $ 3,330 Valuation Assumptions Employee Stock-Based Compensation The Company uses the Black-Scholes option pricing model to determine the fair value of stock option grants to employees and directors and employee stock purchase plan shares. The key input assumptions used to estimate fair value of these awards include the exercise price of the award, the expected option term, the expected volatility of the Company’s stock over the option’s expected term, the risk-free interest rate over the option’s expected term, and the Company’s expected dividend yield, if any. The fair value of share-based payments was estimated on the date of grant using the Black-Scholes option pricing model based on the following weighted average assumptions: Year Ended Year Ended Year Ended Employee ESPP Employee ESPP Employee ESPP Risk-free interest rate 1.9 % 0.5 % 1.7 % 0.3 % 1.9 % 0.2 % Volatility 74.0 % 74.0 % 79.4 % 75.3 % 77.1 % 86.0 % Expected term in years 6.44 0.50 6.38 0.56 6.30 1.25 Expected dividend yield 0.0 % 0.0 % 0.0 % 0.0 % 0.0 % 0.0 % The risk-free interest rate that the Company uses in the option pricing model is based on the U.S. Treasury zero-coupon pre-vesting The Company uses its own historical exercise activity and extrapolates the life cycle of options outstanding to arrive at its estimated expected term for new option grants. The Company uses its own volatility history based on its stock’s trading history for the expected term. The Company measures compensation expense for awards of restricted stock and restricted stock units at fair value on the date of grant and recognizes the expense over the expected vesting period. The fair value for restricted stock and restricted stock unit awards is based on the closing price of the Company’s common stock on the date of grant. As of December 31, 2016, there was $8.5 million of unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted-average period of 2.4 years, and there was $3.1 million of unrecognized compensation cost related to unvested restricted stock and performance stock units, which is expected to be recognized over a weighted-average period of 1.2 years. The fair value for restricted stock units is based on the closing price of the Company’s common stock on the grant date. Non-employee The Company records stock option grants to non-employees, There were no stock option grants to non-employees non-employee In connection with services rendered by non-employees, ESPP In January 2004, the Board of Directors adopted the 2004 ESPP, which was approved by the stockholders in February 2004. Under the 2004 ESPP, statutory employees may purchase common stock of the Company up to a specified maximum amount through payroll deductions. The stock is purchased semi-annually at a price equal to 85% of the fair market value at certain plan-defined dates. The 2004 ESPP was terminated in October 2015. In May 2015, the Board of Directors adopted the 2015 ESPP, which was approved by the stockholders in May 2015. The first purchase period under the 2015 ESPP commenced on November 2, 2015. Under the 2015 ESPP, statutory employees may purchase common stock of the Company up to a specified maximum amount through payroll deductions. The stock is purchased semi-annually at a price equal to 85% of the fair market value at certain plan-defined dates. The Company issued 129,604, 21,167and 19,726 shares of common stock during 2016, 2015 and 2014, respectively, pursuant to the 2004 ESPP at an average price of $7.08, $3.24 and $3.38 per share, in 2016, 2015 and 2014, respectively. At December 31, 2016 the Company had 519,339 shares of common stock reserved for issuance under the 2015 ESPP.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Note 12 — Income Taxes The Company accounts 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. Valuation allowances are established when necessary to reduce the deferred tax assets to the amounts expected to be realized. The Company did not record an income tax provision in the years ended December 31, 2016, 2015, or 2014 because the Company either had net taxable losses in these periods or was able to utilize tax attributes to offset taxable income. For financial statement purposes, income (loss) before taxes includes the following components (in thousands): Years Ended 2016 2015 2014 United States $ 16,453 $ (37,501 ) $ (14,646 ) Foreign — — — Total $ 16,453 $ (37,501 ) $ (14,646 ) The Company recorded the following income tax provision as follows (in thousands): Years Ended 2016 2015 2014 Current: Federal $ — $ — $ — State — — — Total $ — $ — $ — Deferred: Federal $ — $ — $ — State — — — Total $ — $ — $ — Deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The significant components of the Company’s deferred tax assets and liabilities were as follows (in thousands): As of December 31, 2016 2015 2014 Deferred tax assets: Depreciation and amortization $ 766 $ 769 $ 780 Capitalized R&D 11,675 13,150 15,176 Reserves and accruals 10,258 12,899 6,217 Net operating losses 146,961 153,251 148,184 Tax credits 46,998 38,742 34,543 Total deferred tax assets 216,658 218,811 204,900 Less: Valuation allowance (216,658 ) (218,811 ) (204,900 ) Net deferred tax assets $ — $ — $ — Realization of deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Based upon the weight of available evidence, which includes the Company’s historical operating performance, reported cumulative net losses since inception, expected future losses, and difficulty in accurately forecasting the Company’s future results, the Company maintained a full valuation allowance on the net deferred tax assets as of December 31, 2016, 2015 and 2014. The valuation allowance was determined pursuant to the accounting guidance for income taxes, which requires an assessment of both positive and negative evidence when determining whether it is more likely than not that deferred tax assets are recoverable. The Company intends to maintain a full valuation allowance on the U.S. deferred tax assets until sufficient positive evidence exists to support reversal of the valuation allowance. The valuation allowance decreased by $2.2 million in 2016 and increased by $13.9 million in 2015 and $1.0 million in 2014. As a result of certain realization requirements of accounting guidance for stock compensation, the table of deferred tax assets and liabilities shown above does not include certain deferred tax assets at December 31, 2016, 2015 and 2014 that arose directly from tax deductions related to equity compensation in excess of compensation recognized for financial reporting. Approximately $2.0 million of Federal and California net operating losses are related to tax stock option deductions in excess of book deductions. This amount will be credited to stockholders’ equity when it is realized. The following are the Company’s valuation and qualifying accounts (in thousands): Balance at Charged to Charged to Deductions Balance at Year Ended December 31, 2014: Deferred tax valuation allowance $ 203,863 $ 1,037 — — $ 204,900 Year Ended December 31, 2015: Deferred tax valuation allowance $ 204,900 $ 13,911 — — $ 218,811 Year Ended December 31, 2016: Deferred tax valuation allowance $ 218,811 $ (2,153 ) — — $ 216,658 The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate: Years Ended 2016 2015 2014 Tax at federal statutory tax rate 34% (34)% (34)% State income tax, net of federal tax benefit 2% 0% (1)% State Apportionment (7)% 0% 28% Tax credits (net) (32)% (7)% (7)% Deferred tax assets (utilized) not benefited (15)% 37% 7% Stock-based compensation 7% 2% 5% NOL Expiration 9% 2% 2% Other 2% 0% 0% Total 0% 0% 0% The Company had federal net operating loss carryforwards of approximately $388.1 million and apportioned state net operating loss carryforwards of approximately $249.9 million before federal benefit at December 31, 2016. If not utilized, the federal and state operating loss carryforwards will begin to expire in various amounts beginning 2020 and 2017, respectively. The net operating loss carryforwards include deductions for stock options. The Company had general business credit of approximately $44.4 million and $13.6 million for federal and state income tax purposes, respectively, at December 31, 2016. Amounts are comprised of Research and Development Credits and Orphan Drug Credits. If not utilized, the federal carryforwards will expire in various amounts beginning in 2021. The California state credit can be carried forward indefinitely. Since its filing of its 2011 tax return, the Company has claimed the orphan drug credit. For qualifying expenses, the orphan drug credit offers an increased benefit relative to the research and development credit taken in years prior. As required by California state law, the Company apportions income to California based on a “market-based” sourcing approach. Accordingly, the Company’s California apportionment formula is sensitive to changes in the source of the Company’s mix of revenue. In general, under Section 382 of the Internal Revenue Code (“Section 382”), a corporation that undergoes an ‘ownership change’ is subject to limitations on its ability to utilize its pre-change Section 59(e) of the Internal Revenue Code allows a Company to capitalize R&D expenses. The Company did not elect to capitalize R&D expenses in its 2014 tax return as they did not anticipate an ownership change under Section 382. For 2016 and 2015, the Company anticipates foregoing the election in its 2016 and 2015 tax return, respectively, as they do not anticipate an ownership change under Section 382. The Company follows the accounting guidance that prescribes a comprehensive model for how companies should recognize, measure, present, and disclose in their financial statements uncertain tax positions taken or expected to be taken on a tax return. Tax positions are initially recognized in the financial statements when it is more likely than not that the position will be sustained upon examination by the tax authorities. Such tax positions are initially and subsequently measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement with the tax authority assuming full knowledge of the position and relevant facts. The significant jurisdictions in which the Company files income tax returns are the United States and California. For jurisdictions in which tax filings are made, the Company is subject to income tax examination for all fiscal years since inception. The IRS’s Large Business and International Division concluded its audit of the 2009 tax year with no material adjustments. However, in general, the statute of limitations for tax liabilities for all years remains open for the purpose of adjusting the amounts of the losses and credits carried forward from those years. The following table summarizes the activity related to our gross unrecognized tax benefits (in thousands): Years Ended 2016 2015 Balance at the beginning of the year $ 6,715 $ 6,274 Decrease related to prior year tax positions 5 — Increase related to current year tax positions 845 441 Balance at the end of the year $ 7,565 $ 6,715 Included in the balance of unrecognized tax benefits as of December 31, 2016, 2015 and 2014 are $6.3 million, $5.5 million and $5.1 million of tax benefits, respectively, that, if recognized, would result in adjustments to other tax accounts, primarily deferred taxes. The Company recognizes interest accrued related to unrecognized tax benefits and penalties as income tax expense. Related to the unrecognized tax benefits noted above, the Company did not accrue any penalties or interest during 2016, 2015 or 2014. The Company does not expect its unrecognized tax benefit to change materially over the next twelve months.

Interest and Other Income, Net

Interest and Other Income, Net	12 Months Ended
	Dec. 31, 2016
Other Income and Expenses [Abstract]
Interest and Other Income, Net	Note 13 — Interest and Other Income, Net Interest and other income, net for the years ended December 31, 2016, 2015 and 2014, primarily consisted of interest income generated from the Company’s cash, cash equivalents and investments. In 2015, interest income also included net gains realized upon disposal of equipment.

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	Note 14 — Quarterly Financial Data (Unaudited) Quarterly results were as follows (in thousands, except per share data): First Second Third Fourth 2016 Total revenues $ 8,421 $ 5,802 $ 59,047 $ 33,138 Net income (loss) (12,455 ) (11,611 ) 33,362 7,157 Net income (loss) per share — basic $ (0.31 ) $ (0.29 ) $ 0.84 $ 0.18 Net income (loss) per share —diluted $ (0.31 ) $ (0.29 ) $ 0.77 $ 0.16 2015 Total revenues $ 4,414 $ 6,542 $ 7,945 $ 9,757 Net loss (8,872 ) (10,551 ) (8,849 ) (9,229 ) Net (loss) per share — basic and diluted $ (0.23 ) $ (0.27 ) $ (0.23 ) $ (0.24 )

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	Note 15 — Subsequent Events On February 1, 2017, the Company entered into a Royalty Purchase Agreement (the “Royalty Agreement”) with RPI Finance Trust (“RPI”), an entity related to Royalty Pharma. Under the Royalty Agreement, the Company sold a 4.5 percent royalty on potential worldwide sales of omecamtiv mecarbil (and potentially other compounds with the same mechanism of action) that are subject to the Amgen Agreement (as amended) to RPI for a payment of $90.0 million. The royalty rate purchased may increase up to an additional 1 percent under certain circumstances. In addition, RPI has agreed to purchase $10.0 million of Cytokinetics’ common stock pursuant to a concurrently executed Common Stock Purchase Agreement with RPI. In February 2017, the Company provided notice to Amgen of its further exercise of its co-invest co-invest co-funding co-promote From January 1, 2017 to February 23, 2017, the Company sold 185,215 shares pursuant to its CE offering with a weighted average sale price of $11.24 for net proceeds of $2.1 million.

Organization and Significant 23

Organization and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization 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. The Company’s financial statements contemplate the conduct of the Company’s operations in the normal course of business. The Company has incurred an accumulated deficit of $518.3 million since inception and there can be no assurance that the Company will attain profitability. The Company had net income of $16.4 million and net cash provided by operations of $37.0 million for the year ended December 31, 2016. Cash, cash equivalents and investments increased to $163.9 million at December 31, 2016 from $111.6 million at December 31, 2015. The Company anticipates that it will have operating losses and net cash outflows in future periods. The Company is 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 its future plans. The Company’s liquidity will be impaired if sufficient additional capital is not available on terms acceptable to the Company. To date, the Company has funded its operations primarily through sales of its common stock and convertible preferred stock, contract payments under its collaboration agreements, debt financing arrangements, government grants and interest income. Until it achieves profitable operations, the Company intends to continue to fund operations through payments from strategic collaborations, additional sales of equity securities, grants and debt financings. The Company has never generated revenues from commercial sales of its drugs and may not have drugs to market for at least several years, if ever. The Company’s success is dependent on its ability to enter into new strategic collaborations and/or raise additional capital and to successfully develop and market one or more of its drug candidates. As a result, the Company may choose to raise additional capital through equity or debt financings to continue to fund its operations in the future. The Company 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 the Company’s 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 the Company’s future financial results, financial position and cash flows. Based on the current status of its research and development plans, the Company believes that its existing cash, cash equivalents and investments will be sufficient to fund its cash requirements for at least the next 12 months. If, at any time, the Company’s prospects for financing its research and development programs decline, the Company may decide to reduce research and development expenses by delaying, discontinuing or reducing its funding of one or more of its research or development programs. Alternatively, the Company 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. The financial statements do not include any adjustments that might result from the outcome of this uncertainty.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management 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 financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of Cytokinetics and its wholly owned subsidiary and have been prepared in accordance with U.S. generally accepted accounting principles (“US GAAP”). Intercompany transactions and balances have been eliminated in consolidation.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to concentrations of risk consist principally of cash and cash equivalents, investments, long term debt and accounts receivable. The Company’s cash, cash equivalents and investments are invested in deposits with three major financial institutions in the United States. Deposits in these banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any realized losses on its deposits of cash, cash equivalents or investments. The economic turmoil in the United States in recent years, the extraordinary volatility in the stock markets and other current negative macroeconomic indicators could negatively impact the Company’s ability to raise the funds necessary to support its business and may materially adversely affect its business, operating results and financial condition. The Company performs an ongoing credit evaluation of its strategic partners’ financial conditions and generally does not require collateral to secure accounts receivable from its strategic partners. The Company’s exposure to credit risk associated with non-payment Drug candidates developed by the Company may require approvals or clearances from the U.S. Food and Drug Administration (“FDA”) or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s drug candidates will receive any of the required approvals or clearances. If the Company was to be denied approval or clearance or any such approval or clearance was to be delayed, it would have a material adverse impact on the Company. The Company’s operations and employees are located in the United States. In the year ended December 31, 2016, 27% of the Company’s revenues were received from entities located in the United States and 73% were received from a Japanese entity. In the year ended December 31, 2015, 9% of the Company’s revenues were received from entities located in the United States and 91% were received from a Japanese entity. In the year ended December 31, 2014, 10% of the Company’s revenues were received from entities located in the United States and 90% were received from a Japanese entity.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with a maturity of three months or less at the time of purchase to be cash equivalents.
Investments	Investments Available-for-sale available-for-sale available-for-sale available-for-sale Other-than-temporary impairment. available-for-sale
Fair Value of Financial Instruments	Fair Value of Financial Instruments The fair value of financial instruments reflects the amounts that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Cash, accounts payable and accrued liabilities are carried at cost, which approximates fair value given their short-term nature. Marketable securities and cash equivalents, are carried at fair value.
Property and Equipment, net	Property and Equipment, net Property and equipment are stated at cost less accumulated depreciation and are depreciated on a straight-line basis over the estimated useful lives of the related assets, which are generally three years for computer equipment and software, five years for laboratory equipment and office equipment, and seven years for furniture and fixtures. Amortization of leasehold improvements is computed using the straight-line method over the shorter of the remaining lease term or the estimated useful life of the related assets, typically ranging from three to seven years. Upon sale or retirement of assets, the costs and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in operations. Maintenance and repairs are charged to operations as incurred.
Impairment of Long-lived Assets	Impairment of Long-lived Assets In accordance with the accounting guidance for the impairment or disposal of long-lived assets, the Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Under the accounting guidance, an impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is measured as the amount by which the carrying amount of a long-lived asset exceeds its fair value.
Revenue Recognition	Revenue Recognition The accounting guidance for revenue recognition requires that the following criteria must be met before revenue can be recognized: (i) persuasive evidence of an arrangement exists; (ii) delivery has occurred or services have been rendered; (iii) the fee is fixed or determinable; and (iv) collectability is reasonably assured. Determination of whether persuasive evidence of an arrangement exists and whether delivery has occurred or services have been rendered are based on management’s judgments regarding the fixed nature of the fee charged for research performed and milestones met, and the collectability of those fees. Should changes in conditions cause management to determine these criteria are not met for certain future transactions, revenue recognized for any reporting period could be adversely affected. Revenue under the Company’s license and collaboration arrangements is recognized based on the performance requirements of the contract. Research and development revenues, which are earned under agreements with third parties for agreed research and development activities, may include non-refundable 605-25, Revenue Recognition — Multiple-Element Arrangements 605-25”) Upfront, non-refundable non-refundable ASC Topic 605-28, Revenue Recognition — Milestone Method 605-28”), Other contingent event-based payments received for which payment is either contingent solely upon the passage of time or the results of a collaborative partner’s performance are not considered milestones under ASC 605-28. The Company accounts for milestone payments under the provisions of ASC 605-28. Research and development revenues and cost reimbursements are based upon negotiated rates for the Company’s full-time employee equivalents (“FTE”) and actual out-of-pocket Funds received from third parties under grant arrangements are recorded as revenue if the Company is deemed to be the principal participant in the grant arrangement as the activities under the grant are part of the Company’s development program. If the Company is not the principal participant, the grant funds are recorded as a reduction to research and development expense. Grant funds received are not refundable and are recognized when the related qualified research and development costs are incurred and when there is reasonable assurance that the funds will be received. Funds received in advance are recorded as deferred revenue.
Preclinical Studies and Clinical Trial Accruals	Preclinical Studies and Clinical Trial Accruals A substantial portion of the Company’s preclinical studies and all of the Company’s clinical trials have been performed by third-party contract research organizations (“CROs”) and other vendors. For preclinical studies, the significant factors used in estimating accruals include the percentage of work completed to date and contract milestones achieved. For clinical trial expenses, the significant factors used in estimating accruals include the number of patients enrolled, duration of enrollment and percentage of work completed to date. The Company monitors patient enrollment levels and related activities to the extent practicable through internal reviews, correspondence and status meetings with CROs, and review of contractual terms. The Company’s estimates are dependent on the timeliness and accuracy of data provided by its CROs and other vendors. If the Company has incomplete or inaccurate data, it may under- or overestimate activity levels associated with various studies or trials at a given point in time. In this event, it could record adjustments to research and development expenses in future periods when the actual activity level becomes known.
Research and Development Expenditures	Research and Development Expenditures Research and development costs are charged to operations as incurred. Research and development expenses consist primarily of clinical manufacturing costs, preclinical study expenses, consulting and other third party costs, employee compensation, supplies and materials, allocation of overhead and occupancy costs, facilities costs and depreciation of equipment.
Income Taxes	Income Taxes The Company accounts 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. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company also follows the accounting guidance that defines the threshold for recognizing the benefits of tax return positions in the financial statements as “more-likely-than-not”
Comprehensive Income (Loss)	Comprehensive Income (Loss) The Company follows the accounting standards for the reporting and presentation of comprehensive income (loss) and its components in a continuous statement of comprehensive income (loss). Comprehensive income (loss) includes all changes in stockholders’ equity during a period from non-owner
Segment Reporting	Segment Reporting The Company has determined that it operates in only one segment — the discovery and development of first-in-class
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based payment awards made to employees and directors, including employee stock options and employee stock purchases by measuring the stock-based compensation cost at the grant date based on the calculated fair value of the award, and recognizing expense on a straight-line basis over the employee’s requisite service period, generally the vesting period of the award. Stock compensation for non-employees The Company reviews the valuation assumptions at each grant date and, as a result, from time to time it will likely change the valuation assumptions it uses to value stock based awards granted in future periods. The assumptions used in calculating the fair value of share-based payment awards represent management’s best estimates at the time, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if conditions change and the management uses different assumptions, the Company’s stock-based compensation expense could be materially different in the future. In addition, the Company is required to estimate the expected forfeiture rate and recognize expense only for those shares expected to vest. If the actual forfeiture rate is materially different from management’s estimate, stock-based compensation expense could be significantly different from what has been recorded in the current period.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2016, the FASB issued ASU 2016-15, ‘Statement of cash flows (Topic 230): Classification of certain cash receipts and cash payments’. ASU 2016-15 2016-15 In June 2016, the FASB issued ASU 2016-13, ‘Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments. ASU 2016-13 2016-13 In March 2016, the FASB issued ASU 2016-09, Stock compensation (Topic 718). ASU 2016-09 . 2016-09 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 right-to-use . 2016-02 In January 2016, the FASB issued ASU 2016-01, Financial instruments (Subtopic 825-10). ASU 2016-01 2016-01 2016-01 In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40): ASU 2014-15 2014-15 2014-12, 2014-12 In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Calculation of Basic and Diluted Net Income (Loss) Per Share	The following is the calculation of basic and diluted net income (loss) per share (in thousands, except per share data): Years Ended December 31, 2016 2015 2014 Net income (loss) $ 16,453 $ (37,501 ) $ (14,646 ) Weighted-average shares used in computing net income (loss) per share — basic 39,943 38,814 35,709 Effect of dilutive securities: Warrants to purchase common stock 2,019 — — Options to purchase common stock 409 — — Restricted stock units 181 — — Shares issuable related to the ESPP 9 — — Dilutive potential common shares 2,618 — — Weighted-average shares used in computing net income (loss) per share — diluted 42,561 38,814 35,709 Net income (loss) per share — basic $ 0.41 $ (0.97 ) $ (0.41 ) Net income (loss) per share — diluted $ 0.39 $ (0.97 ) $ (0.41 )
Instruments Excluded from the Computation of Diluted Net Income (Loss) Per Share	The following instruments were excluded from the computation of diluted net income (loss) per share for the periods presented because their effect would have been antidilutive (in thousands): December 31, 2016 2015 2014 Options to purchase common stock 3,688 4,835 3,298 Warrants to purchase common stock — 5,641 6,691 Restricted and Performance stock units — 757 63 Shares issuable related to the ESPP — 16 15 Total shares 3,688 11,249 10,067

Supplementary Cash Flow Data (T

Supplementary Cash Flow Data (Tables)	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental cash flow information was as follows (in thousands): Years Ended 2016 2015 2014 Cash paid for interest $ 1,899 $ 94 $ — Cash paid for income taxes 1 1 1 Significant non-cash Debt discount netted against proceeds from long term debt, recorded in equity 288 282 — Interest paid on the long-term debt, at inception 63 41 — Purchases of property and equipment through accounts payable (320 ) (147 ) 170 Purchases of property and equipment through accrued liabilities (747 ) (2 ) 27

Cash Equivalents and Investme26

Cash Equivalents and Investments (Tables)	12 Months Ended
	Dec. 31, 2016
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 December 31, 2016 and 2015 were as follows (in thousands): December 31, 2016 Amortized Unrealized Unrealized Fair Maturity Cash equivalents — U. S. Treasury securities and money market funds $ 55,658 $ — $ — $ 55,658 Short-term investments — U.S. Treasury securities $ 89,396 $ 2 $ (23 ) $ 89,375 1/2017 — 12/2017 Long-term investments — Equity and U.S. Treasury securities $ 7,513 $ 176 $ (17 ) $ 7,672 2/2018 — 3/2018 December 31, 2015 Amortized Unrealized Unrealized Fair Maturity Cash equivalents — money market funds $ 63,136 $ — $ — $ 63,136 Short-term investments — U.S. Treasury securities $ 46,395 $ 1 $ (30 ) $ 46,366 2/2016 —8/2016 Long-term investments — equity securities $ — $ 179 $ — $ 179
Summary of Interest Income	Interest income was as follows (in thousands): Years Ended 2016 2015 2014 Interest income $ 449 $ 156 $ 101

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
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 December 31, 2016 and 2015 are classified in the table below in one of the three categories described above (in thousands): December 31, 2016 Fair Value Measurements Using Assets Level 1 Level 2 Level 3 Assets: Money market funds $ 52,657 $ — $ — $ 52,657 U.S. Treasury securities 99,872 — — 99,872 Equity securities 176 — — 176 Total $ 152,705 $ — $ — $ 152,705 Amounts included in: Cash and cash equivalents $ 55,658 $ — $ — $ 55,658 Short-term investments 89,375 — — 89,375 Long-term investments 7,672 — — 7,672 Total $ 152,705 $ — $ — $ 152,705 December 31, 2015 Fair Value Measurements Using Assets Level 1 Level 2 Level 3 Assets: Money market funds $ 63,136 $ — $ — $ 63,136 U.S. Treasury securities 46,366 — — 46,366 Equity securities 179 — — 179 Total $ 109,681 $ — $ — $ 109,681 Amounts included in: Cash and cash equivalents $ 63,136 $ — $ — $ 63,136 Short-term investments 46,366 — — 46,366 Long-term investments 179 — — 179 Total $ 109,681 $ — $ — $ 109,681

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Property and Equipment Balances	Property and equipment balances were as follows (in thousands): December 31, 2016 2015 Property and equipment, net: Laboratory equipment $ 16,742 $ 15,713 Computer equipment and software 2,699 2,510 Office equipment, furniture and fixtures 856 945 Leasehold improvements 4,458 3,425 Total property and equipment 24,755 22,593 Less: Accumulated depreciation and amortization (21,118 ) (20,842 ) Total property and equipment, net $ 3,637 $ 1,751
Summary of Accrued Liabilities	Accrued liabilities were as follows (in thousands): December 31, 2016 2015 Accrued liabilities: Clinical and preclinical costs $ 10,092 $ 3,446 Bonus 3,800 2,720 Other payroll related 1,888 1,464 Other accrued expenses 1,595 791 Leasehold improvements 672 — Total accrued liabilities $ 18,047 $ 8,421

Related Parties and Related P29

Related Parties and Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2016
Astellas [Member]
Revenue from Related Party	Research and development revenue from Astellas was as follows (in thousands): Year Ended Year Ended Year Ended License Revenues from Related Parties $ 62,171 $ 13,918 $ 9,835 Research and development revenues with related parties: Reimbursement of internal costs 6,111 6,210 — Reimbursement of other costs 6,999 5,974 — Research and development milestone fees 2,000 — 15,000 Total research and development revenue with related parties from Astellas $ 15,110 $ 12,184 $ 15,000 Research and development revenues: Reimbursement of internal costs — — 8,939 Reimbursement of other costs — — 6,452 Research and development milestone fees — — 2,000 Total research and development revenue from Astellas — — 17,391 Total Revenue from Astellas $ 77,281 $ 26,102 $ 42,226
Schedule of Arrangement Consideration under 2016 Amendment Related to CK-107 and Research	Arrangement Consideration under the 2016 Astellas Amendment related to CK-2127107 Arrangement Amendment Fee $ 35.0 Accelerated milestone payment 15.0 Total Upfront Consideration 50.0 Additional Research Services 5.1 ALS Development Services 39.1 Total Committed Consideration 44.2 Total Consideration $ 94.2
Schedule Represents Allocation of Arrangement Consideration, and Revenue Recognition	Allocation of arrangement consideration, and revenue recognition (in millions): Allocated Upfront Revenue Units of Accounting: ALS License $ 74.9 $ 50.0 $ 24.9 Research and ALS Development Services 19.3 — 19.3 Total consideration $ 94.2 $ 50.0 $ 44.2
Amgen [Member]
Revenue from Related Party	Revenue from Amgen was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Research and development revenues from related parties, net: Reimbursement of internal costs $ 2,466 $ 2,460 $ 4,260 Research and development milestone fees 26,666 — — Co-invest (1,250 ) — — Allocated consideration — 21 278 Total Research and development revenues from related parties, net 27,882 2,481 4,538 Total net revenues from Amgen $ 27,882 $ 2,481 $ 4,538

Other Research and Developmen30

Other Research and Development Revenue Arrangements Grants (Tables)	12 Months Ended
	Dec. 31, 2016
Summary of Total Grant Revenues	Total grant revenues were as follows (in thousands): Years Ended 2016 2015 2014 ALSA grant revenue $ 1,084 $ 75 $ — Other grant revenue — — 75 Total grant revenue $ 1,084 $ 75 $ 75
MyoKardia [Member]
Summary of Reimbursed Expenses	Research and development revenue from MyoKardia was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Research and development milestone fees $ 150 $ — $ 100 Research and development revenue from Myokardia $ 150 $ — $ 100

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Long Term Debt and Unamortized Debt Discount	Long-term debt and unamortized debt discount balances are as follows (in thousands): December 31, 2016 2015 Notes payable, gross $ 30,000 $ 15,000 Less: Unamortized debt discount (472 ) (389 ) Accretion of final exit fee 353 28 Carrying value of notes payable 29,881 14,639 Less: Current portion of long-term debt (2,500 ) — Long-term debt $ 27,381 $ 14,639
Schedule of Future Minimum Payments under Loan	Future minimum payments under the Loan, as of December 31, 2016 are as follows (in thousands): 2017 $ 4,768 2018 11,743 2019 10,982 2020 8,938 Total minimum payments 36,431 Less: Interest and final payment (6,431 ) Notes payable, gross $ 30,000

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Rent Expense	Rent expense was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Rent expense $ 3,448 $ 3,297 $ 3,338
Future Minimum Lease Payments under Noncancelable Operating Leases	As of December 31, 2016, future minimum lease payments under noncancelable operating leases were as follows (in thousands): 2017 $ 3,703 2018 1,860 2019 — 2020 — 2021 — Thereafter — Total $ 5,563
Amgen [Member]
Future Minimum Payments for Co-investment	As of December 31, 2016, future minimum payments due to Amgen were as follows (in thousands): 2017 $ 5,000 2018 3,750 Total $ 8,750

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Outstanding Warrants	Outstanding warrants as of December 31, 2016 were as follows: Number Exercise Expiration Issued 6/25/2012 4,104,966 $ 5.28 06/25/17 Issued 10/19/2015 65,189 $ 6.90 10/19/20 Issued 02/10/2016 68,285 $ 6.59 02/10/21
Summary of Stock Option Activity	Activity under the Equity Incentive Plan was as follows: Shares Stock Options Weighted Weighted Aggregate Balance at December 31, 2013 2,161,829 2,449,365 $ 15.15 Options granted (944,831 ) 944,831 8.80 Restricted stock units granted (43,500 ) — — Options exercised — (390 ) 6.00 Options forfeited/expired 95,980 (95,980 ) 39.74 Restricted stock units forfeited 1,000 — — Balance at December 31, 2014 1,270,478 3,297,826 $ 12.62 Increase in authorized shares 3,130,000 — — Options granted (1,175,730 ) 1,175,730 7.62 Restricted stock units granted (739,000 ) — — Options exercised — (68,635 ) 6.22 Options forfeited/expired 326,762 (326,762 ) 16.83 Restricted stock units forfeited 3,500 — — Balance at December 31, 2015 2,816,010 4,078,159 $ 10.94 Options granted (1,446,675 ) 1,446,675 7.10 Restricted stock units granted (47,000 ) — — Options exercised — (74,556 ) 6.75 Options forfeited/expired 257,465 (257,465 ) 24.25 Restricted stock units forfeited 8,500 — — Balance at December 31, 2016 1,588,300 5,192,813 $ 9.27 6.83 $ 21,294 Exercisable at December 31, 2016 3,364,286 $ 10.24 5.83 $ 12,771 Vested and expected to vest as of December 31, 2016 5,147,387 $ 9.29 6.81 $ 21,075
Stock-Based Compensation Related to Stock Options, Restricted Stock Awards, Restricted Stock Unit, and Employee Stock Purchases	The following table summarizes stock-based compensation related to stock options, restricted stock awards, restricted stock unit, and employee stock purchases (in thousands): Years Ended December 31, 2016 2015 2014 Research and development $ 4,252 $ 1,828 $ 1,361 General and administrative 2,894 2,739 1,969 Stock-based compensation included in operating expenses $ 7,146 $ 4,567 $ 3,330
Fair Value of Share-Based Payments was Estimated on Date of Grant Using Black-Scholes Option Pricing Model Based on Weighted Average Assumptions	The fair value of share-based payments was estimated on the date of grant using the Black-Scholes option pricing model based on the following weighted average assumptions: Year Ended Year Ended Year Ended Employee ESPP Employee ESPP Employee ESPP Risk-free interest rate 1.9 % 0.5 % 1.7 % 0.3 % 1.9 % 0.2 % Volatility 74.0 % 74.0 % 79.4 % 75.3 % 77.1 % 86.0 % Expected term in years 6.44 0.50 6.38 0.56 6.30 1.25 Expected dividend yield 0.0 % 0.0 % 0.0 % 0.0 % 0.0 % 0.0 %
Restricted Stock Units [Member]
Summary of Stock Unit Activity	Restricted stock unit activity was as follows: Number of Weighted Restricted stock units outstanding at December 31, 2013 41,663 $ 6.00 Restricted stock units granted 43,500 9.65 Restricted stock units vested (20,833 ) 6.00 Restricted stock units forfeited (1,000 ) 6.00 Unvested restricted stock units outstanding at December 31, 2014 63,330 8.51 Restricted stock units granted 54,000 7.96 Restricted stock units vested (42,078 ) 7.82 Restricted stock units forfeited (3,500 ) 8.68 Unvested restricted stock units outstanding at December 31, 2015 71,752 8.49 Restricted stock units granted 47,000 6.67 Restricted stock units vested (45,750 ) 8.69 Restricted stock units forfeited (8,500 ) 7.20 Unvested restricted stock units outstanding at December 31, 2016 64,502 7.19
Performance Restricted Stock Units [Member]
Summary of Stock Unit Activity	Performance stock unit activity was as follows: Number of Weighted Performance stock units outstanding at December 31, 2014 — $ — Restricted stock units granted 685,000 7.00 Restricted stock units vested — — Restricted stock units forfeited — — Unvested restricted stock units outstanding at December 31, 2015 685,000 7.00 Restricted stock units granted — — Restricted stock units vested — — Restricted stock units forfeited — — Unvested restricted stock units outstanding at December 31, 2016 685,000 $ 7.00

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income (Loss) Before Taxes	For financial statement purposes, income (loss) before taxes includes the following components (in thousands): Years Ended 2016 2015 2014 United States $ 16,453 $ (37,501 ) $ (14,646 ) Foreign — — — Total $ 16,453 $ (37,501 ) $ (14,646 )
Company Recorded Income Tax Provision	The Company recorded the following income tax provision as follows (in thousands): Years Ended 2016 2015 2014 Current: Federal $ — $ — $ — State — — — Total $ — $ — $ — Deferred: Federal $ — $ — $ — State — — — Total $ — $ — $ —
Company's Deferred Tax Assets and Liabilities	The significant components of the Company’s deferred tax assets and liabilities were as follows (in thousands): As of December 31, 2016 2015 2014 Deferred tax assets: Depreciation and amortization $ 766 $ 769 $ 780 Capitalized R&D 11,675 13,150 15,176 Reserves and accruals 10,258 12,899 6,217 Net operating losses 146,961 153,251 148,184 Tax credits 46,998 38,742 34,543 Total deferred tax assets 216,658 218,811 204,900 Less: Valuation allowance (216,658 ) (218,811 ) (204,900 ) Net deferred tax assets $ — $ — $ —
Company's Valuation and Qualifying Accounts	The following are the Company’s valuation and qualifying accounts (in thousands): Balance at Charged to Charged to Deductions Balance at Year Ended December 31, 2014: Deferred tax valuation allowance $ 203,863 $ 1,037 — — $ 204,900 Year Ended December 31, 2015: Deferred tax valuation allowance $ 204,900 $ 13,911 — — $ 218,811 Year Ended December 31, 2016: Deferred tax valuation allowance $ 218,811 $ (2,153 ) — — $ 216,658
Reconciliation of Statutory Federal Income Tax Rate to Effective Tax Rate	The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate: Years Ended 2016 2015 2014 Tax at federal statutory tax rate 34% (34)% (34)% State income tax, net of federal tax benefit 2% 0% (1)% State Apportionment (7)% 0% 28% Tax credits (net) (32)% (7)% (7)% Deferred tax assets (utilized) not benefited (15)% 37% 7% Stock-based compensation 7% 2% 5% NOL Expiration 9% 2% 2% Other 2% 0% 0% Total 0% 0% 0%
Schedule of Activity Related to our Gross Unrecognized Tax Benefits	The following table summarizes the activity related to our gross unrecognized tax benefits (in thousands): Years Ended 2016 2015 Balance at the beginning of the year $ 6,715 $ 6,274 Decrease related to prior year tax positions 5 — Increase related to current year tax positions 845 441 Balance at the end of the year $ 7,565 $ 6,715

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results	Quarterly results were as follows (in thousands, except per share data): First Second Third Fourth 2016 Total revenues $ 8,421 $ 5,802 $ 59,047 $ 33,138 Net income (loss) (12,455 ) (11,611 ) 33,362 7,157 Net income (loss) per share — basic $ (0.31 ) $ (0.29 ) $ 0.84 $ 0.18 Net income (loss) per share —diluted $ (0.31 ) $ (0.29 ) $ 0.77 $ 0.16 2015 Total revenues $ 4,414 $ 6,542 $ 7,945 $ 9,757 Net loss (8,872 ) (10,551 ) (8,849 ) (9,229 ) Net (loss) per share — basic and diluted $ (0.23 ) $ (0.27 ) $ (0.23 ) $ (0.24 )

Organization and Significant 36

Organization and Significant Accounting Policies - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2016USD ($)Financial_Institution	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2016USD ($)Financial_InstitutionSegment	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit incurred	$ (518,291,000)				$ (534,744,000)				$ (518,291,000)	$ (534,744,000)
Net income	7,157,000	$ 33,362,000	$ (11,611,000)	$ (12,455,000)	(9,229,000)	$ (8,849,000)	$ (10,551,000)	$ (8,872,000)	16,453,000	(37,501,000)	$ (14,646,000)
Net cash provided by (used in) operating activities									36,982,000	4,883,000	$ (44,843,000)
Cash, cash equivalents and investments	$ 163,900,000				111,600,000				$ 163,900,000	$ 111,600,000
Cash requirements term									12 months
Number of major financial institutions | Financial_Institution	3								3
Percentage of income tax likely to be realized									50.00%
Number of reporting segment | Segment									1
Computer Equipment and Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									3 years
Laboratory Equipment and Office Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									5 years
Furniture and Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									7 years
Leasehold Improvements [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									7 years
Leasehold Improvements [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									3 years
United States [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenues derived									27.00%	9.00%	10.00%
Japanese [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenues derived									73.00%	91.00%	90.00%
Amgen [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable due	$ 0				0				$ 0	$ 0
Amgen [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenues derived									26.00%	9.00%	10.00%
Astellas [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable due	$ 0				$ 0				$ 0	$ 0
Astellas [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenues derived									73.00%	91.00%	90.00%

Net Income (Loss) Per Share - C

Net Income (Loss) Per Share - Calculation of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income (loss)	$ 7,157	$ 33,362	$ (11,611)	$ (12,455)	$ (9,229)	$ (8,849)	$ (10,551)	$ (8,872)	$ 16,453	$ (37,501)	$ (14,646)
Weighted-average shares used in computing net income (loss) per share - basic									39,943	38,814	35,709
Effect of dilutive securities:
Warrants to purchase common stock									2,019	0	0
Options to purchase common stock									409	0	0
Restricted stock units									181	0	0
Shares issuable related to the ESPP									9	0	0
Dilutive potential common shares									2,618	0	0
Weighted-average shares used in computing net income (loss) per share - diluted									42,561	38,814	35,709
Net income (loss) per share - basic	$ 0.18	$ 0.84	$ (0.29)	$ (0.31)					$ 0.41	$ (0.97)	$ (0.41)
Net income (loss) per share - diluted	$ 0.16	$ 0.77	$ (0.29)	$ (0.31)					$ 0.39	$ (0.97)	$ (0.41)

Net Income (Loss) Per Share - I

Net Income (Loss) Per Share - Instruments Excluded from the Computation of Diluted Net Income (Loss) Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	3,688	11,249	10,067
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	3,688	4,835	3,298
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	0	5,641	6,691
Restricted and Performance Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	0	757	63
ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	0	16	15

Supplementary Cash Flow Data -

Supplementary Cash Flow Data - Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 1,899	$ 94	$ 0
Cash paid for income taxes	1	1	1
Significant non-cash investing and financing activities:
Debt discount netted against proceeds from long term debt, recorded in equity	288	282	0
Interest paid on the long-term debt, at inception	63	41	0
Purchases of property and equipment through accounts payable	(320)	(147)	170
Purchases of property and equipment through accrued liabilities	$ (747)	$ (2)	$ 27

Cash Equivalents and Investme40

Cash Equivalents and Investments - Amortized Cost and Fair Value of Cash Equivalents and Available for Sale Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Cash Equivalents [Member] | Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Amortized Cost		$ 63,136
Unrealized Gains		0
Unrealized Losses		0
Fair Value		63,136
Cash Equivalents [Member] | US Treasury Securities and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 55,658
Unrealized Gains	0
Unrealized Losses	0
Fair Value	55,658
Short-term Investments [Member] | U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
Amortized Cost	89,396	46,395
Unrealized Gains	2	1
Unrealized Losses	(23)	(30)
Fair Value	$ 89,375	$ 46,366
Short-term Investments [Member] | Minimum [Member] | U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
Maturity Dates	Jan. 31, 2017	Feb. 29, 2016
Short-term Investments [Member] | Maximum [Member] | U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
Maturity Dates	Dec. 31, 2017	Aug. 31, 2016
Long-term Investments [Member] | Equity and U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 7,513
Unrealized Gains	176
Unrealized Losses	(17)
Fair Value	$ 7,672
Long-term Investments [Member] | Equity Securities [Member]
Cash and Cash Equivalents [Line Items]
Amortized Cost		$ 0
Unrealized Gains		179
Unrealized Losses		0
Fair Value		$ 179
Long-term Investments [Member] | Minimum [Member] | Equity and U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
Maturity Dates	Feb. 28, 2018
Long-term Investments [Member] | Maximum [Member] | Equity and U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
Maturity Dates	Mar. 31, 2018

Cash Equivalents and Investme41

Cash Equivalents and Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Investments in continuous unrealized loss position for 12 months or longer	$ 0
U.S. Treasury Securities [Member]
Cash and Cash Equivalents [Line Items]
U.S. Treasury securities maturity start date	Jan. 1, 2017
U.S. Treasury securities maturity end date	Feb. 23, 2017
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Unrealized losses	$ 23,000	$ 30,000

Cash Equivalents and Investme42

Cash Equivalents and Investments - Summary of Interest Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Interest income	$ 449	$ 156	$ 101

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	$ 152,705	$ 109,681
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	52,657	63,136
U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	99,872	46,366
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	176	179
Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	7,672	179
Fair Value Measurements Using Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	152,705	109,681
Fair Value Measurements Using Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	52,657	63,136
Fair Value Measurements Using Level 1 [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	99,872	46,366
Fair Value Measurements Using Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	176	179
Fair Value Measurements Using Level 1 [Member] | Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	7,672	179
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
Fair Value Measurements Using Level 2 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value Measurements Using Level 2 [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value Measurements Using Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value Measurements Using Level 2 [Member] | Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
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
Fair Value Measurements Using Level 3 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value Measurements Using Level 3 [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value Measurements Using Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value Measurements Using Level 3 [Member] | Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	55,658	63,136
Cash and Cash Equivalents [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	55,658	63,136
Cash and Cash Equivalents [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
Cash and Cash Equivalents [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
Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	89,375	46,366
Short-term Investments [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	89,375	46,366
Short-term Investments [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
Short-term Investments [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

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term debt, fair value	$ 29,900,000	$ 14,600,000
Fair Value Measurements Using Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets measured at fair value on a recurring basis	0	0
Fair Value Measurements Using Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets measured at fair value on a recurring basis	$ 0	$ 0

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment Balances (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property and equipment, net:
Total property and equipment	$ 24,755	$ 22,593
Less: Accumulated depreciation and amortization	(21,118)	(20,842)
Total property and equipment, net	3,637	1,751
Laboratory Equipment [Member]
Property and equipment, net:
Total property and equipment	16,742	15,713
Computer Equipment and Software [Member]
Property and equipment, net:
Total property and equipment	2,699	2,510
Office Equipment, Furniture and Fixtures [Member]
Property and equipment, net:
Total property and equipment	856	945
Leasehold Improvements [Member]
Property and equipment, net:
Total property and equipment	$ 4,458	$ 3,425

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Depreciation expense	$ 0.7	$ 0.6	$ 0.5
Interest receivable on cash equivalents and investments	0.2	0.2
Employer contributions under the plan	$ 0.5	$ 0.4	$ 0.3

Balance Sheet Components - Su47

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accrued liabilities:
Clinical and preclinical costs	$ 10,092	$ 3,446
Bonus	3,800	2,720
Other payroll related	1,888	1,464
Other accrued expenses	1,595	791
Leasehold improvements	672	0
Total accrued liabilities	$ 18,047	$ 8,421

Related Parties and Related P48

Related Parties and Related Party Transactions - Additional Information (Detail)	Jul. 27, 2016USD ($)	Feb. 28, 2017USD ($)	Dec. 31, 2016USD ($)Installment	Oct. 31, 2016USD ($)	Jan. 31, 2015USD ($)	Dec. 31, 2014USD ($)$ / sharesshares	Jul. 31, 2013USD ($)	Jun. 30, 2013USD ($)$ / sharesshares	Feb. 23, 2017USD ($)shares	Dec. 31, 2013USD ($)	Dec. 31, 2016USD ($)Installment	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)$ / shares	Jun. 25, 2012$ / shares
Related Party Transaction [Line Items]
License revenues from related parties											$ 62,171,000	$ 13,918,000	$ 0
Per share price of common stock | $ / shares						$ 8							$ 8	$ 4.56
Aggregate purchase price											0	8,673,000	$ 48,971,000
Research and development revenue from related parties											42,994,000	14,665,000	19,538,000
Related party accounts receivable			$ 24,000								24,000	12,000
License revenues											0	0	9,836,000
Percentage of shared costs	25.00%
Subsequent Events [Member]
Related Party Transaction [Line Items]
Common stock, shares issued in period | shares									993,408
Aggregate purchase price									$ 11,000,000
Amgen [Member]
Related Party Transaction [Line Items]
License revenues from related parties								$ 15,000,000		$ 17,200,000
Common stock, shares issued in period | shares								1,404,100
Per share price of common stock | $ / shares								$ 7.12
Aggregate purchase price								$ 10,000,000
Common stock fair value											$ 7,500,000
Research and development revenues from related parties													300,000
Collaboration agreement extend term											2,016
Pre-commercialization milestone payments eligible to receive											$ 300,000,000
Revenue recognized for milestones achieved											26,666,000
Co-fund costs requirement value											$ 40,000,000
Number of quarterly installments of co-fund payments | Installment			8								8
Co-invest option exercised amount			$ 10,000,000								$ 10,000,000
Percentage of incremental royalty receivable on annual net sales			1.00%								1.00%
Co-invest option payment											$ 1,250,000	0	0
Research and development revenue from related parties											27,882,000	2,481,000	4,538,000
Related party accounts receivable			$ 0								0	0
Amgen [Member] | Collaboration Revenue [Member]
Related Party Transaction [Line Items]
Co-invest option payment											1,300,000
Amgen [Member] | Subsequent Events [Member]
Related Party Transaction [Line Items]
Co-fund costs requirement value		$ 40,000,000
Co-invest option exercised amount		$ 30,000,000
Amgen [Member] | License and Services [Member]
Related Party Transaction [Line Items]
Deferred revenue			2,500,000								2,500,000
Amgen [Member] | Galactic HF [Member]
Related Party Transaction [Line Items]
Revenue recognized for milestones achieved											26,700,000
Astellas [Member]
Related Party Transaction [Line Items]
License revenues from related parties											62,171,000	13,918,000	9,835,000
Revenue recognized for milestones achieved											2,000,000	0	15,000,000
Research and development revenue from related parties											15,110,000	12,184,000	15,000,000
Upfront payment received							$ 16,000,000
Potential amount receivable under collaboration agreement							$ 24,000,000
Research and development collaboration agreement period							2 years
Reimbursement costs											0	3,500,000	$ 15,400,000
Percentage of shared costs	75.00%
Upfront Revenue Recognition	$ 50,000,000										50,000,000
Revenue Recognition over Performance Period	44,200,000										44,200,000
Allocated Consideration	$ 94,200,000										94,200,000
Astellas [Member] | License Revenue [Member]
Related Party Transaction [Line Items]
Deferred revenue			0								$ 0
2014 Agreement [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Common stock, shares issued in period | shares						2,040,816
Per share price of common stock | $ / shares						$ 4.90							$ 4.90
Aggregate purchase price						$ 10,000,000
Common stock fair value						9,100,000
Upfront payment received					$ 30,000,000
Potential amount receivable under collaboration agreement						20,000,000
Research and development collaboration agreement period											2 years
Reimbursement costs						0					$ 13,000,000	8,700,000
Amount received as milestone payment					$ 15,000,000
2014 Agreement [Member] | Astellas [Member] | License and Services [Member]
Related Party Transaction [Line Items]
Deferred revenue						$ 900,000							$ 900,000
2014 Agreement [Member] | Astellas [Member] | License Revenue [Member]
Related Party Transaction [Line Items]
Deferred revenue			7,200,000								7,200,000
2016 Astellas Amendment [Member]
Related Party Transaction [Line Items]
License revenues											50,100,000
Non-refundable option fee				$ 15,000,000
Premium percentage	100.00%
2016 Astellas Amendment [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Deferred revenue			23,100,000								23,100,000	20,400,000
Potential amount receivable under collaboration agreement	$ 41,800,000
Reimbursement costs											100,000
Amount received as milestone payment	15,000,000
Upfront amendment fee	35,000,000
Accounts receivable due from related parties			$ 0								0	0
2016 Astellas Amendment [Member] | Astellas [Member] | Phase 2 Clinical Development [Member]
Related Party Transaction [Line Items]
Potential amount receivable under collaboration agreement	36,600,000
2016 Astellas Amendment [Member] | Astellas [Member] | Continuing Research Collaboration [Member]
Related Party Transaction [Line Items]
Potential amount receivable under collaboration agreement	5,200,000
Maximum [Member] | Amgen [Member]
Related Party Transaction [Line Items]
Commercialization milestone payments eligible to receive											300,000,000
Maximum [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Research milestone payments											2,000,000
Maximum [Member] | 2016 Astellas Amendment [Member] | Astellas [Member] | Tirasemtiv Option [Member]
Related Party Transaction [Line Items]
Amount received as milestone payment	30,000,000
Option exercise payment to be received	80,000,000
Maximum [Member] | Initial Indication [Member]
Related Party Transaction [Line Items]
Milestone payments to be received	100,000,000
Maximum [Member] | Subsequent Indication [Member]
Related Party Transaction [Line Items]
Milestone payments to be received	50,000,000
Minimum [Member] | 2016 Astellas Amendment [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Potential amount receivable under collaboration agreement	600,000,000
Minimum [Member] | 2016 Astellas Amendment [Member] | Astellas [Member] | Tirasemtiv Option [Member]
Related Party Transaction [Line Items]
Option exercise payment to be received	25,000,000
Proportional Performance Model [Member]
Related Party Transaction [Line Items]
License revenues											12,100,000	11,600,000	0
Proportional Performance Model [Member] | Astellas [Member]
Related Party Transaction [Line Items]
License revenues											0	$ 2,300,000	$ 9,800,000
Early Development [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Revenue recognized for milestones achieved											2,000,000
Non- neuromuscular Indications [Member] | Maximum [Member] | 2016 Astellas Amendment [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Potential amount receivable under collaboration agreement	95,000,000
Commercial Milestones [Member] | Maximum [Member] | 2016 Astellas Amendment [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Potential amount receivable under collaboration agreement	200,000,000
SMA and Other Neuromuscular Indications [Member] | Minimum [Member] | 2016 Astellas Amendment [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Potential amount receivable under collaboration agreement	100,000,000
Tirasemtiv License [Member] | 2016 Astellas Amendment [Member] | Astellas [Member] | Tirasemtiv Option [Member]
Related Party Transaction [Line Items]
Revenue recognized for milestones achieved	15,000,000
ALS License [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Upfront Revenue Recognition	50,000,000										50,000,000
Revenue Recognition over Performance Period	24,900,000										24,900,000
Allocated Consideration	74,900,000										74,900,000
Research and ALS Development Services [Member] | Astellas [Member]
Related Party Transaction [Line Items]
Upfront Revenue Recognition											0
Revenue Recognition over Performance Period											19,300,000
Allocated Consideration	$ 19,300,000										$ 19,300,000

Related Parties and Related P49

Related Parties and Related Party Transactions - Revenue from Related Party (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
License revenues from related parties			$ 62,171	$ 13,918	$ 0
Research and development revenues from related parties, net:
Total research and development revenue with related parties from Astellas			42,994	14,665	19,538
Research and development revenues:
Total revenues			106,407	28,658	46,940
Amgen [Member]
Related Party Transaction [Line Items]
License revenues from related parties	$ 15,000	$ 17,200
Research and development revenues from related parties, net:
Reimbursement of internal costs			2,466	2,460	4,260
Research and development milestone fees			26,666
Co-invest option payment			(1,250)	0	0
Allocated consideration			0	21	278
Total research and development revenue with related parties from Astellas			27,882	2,481	4,538
Research and development revenues:
Total revenues			27,882	2,481	4,538
Astellas [Member]
Related Party Transaction [Line Items]
License revenues from related parties			62,171	13,918	9,835
Research and development revenues from related parties, net:
Reimbursement of internal costs			6,111	6,210	0
Reimbursement of other costs			6,999	5,974	0
Research and development milestone fees			2,000	0	15,000
Total research and development revenue with related parties from Astellas			15,110	12,184	15,000
Research and development revenues:
Reimbursement of internal costs			0	0	8,939
Reimbursement of other costs			0	0	6,452
Research and development milestone fees			0	0	2,000
Total research and development revenue			0	0	17,391
Total revenues			$ 77,281	$ 26,102	$ 42,226

Related Parties and Related P50

Related Parties and Related Party Transactions - Schedule of Arrangement Consideration under 2016 Amendment Related to CK-107 and Research (Detail) - Astellas [Member] - USD ($) $ in Millions	Jul. 27, 2016	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Total upfront consideration	$ 50	$ 50
Total committed consideration	44.2	44.2
Total Consideration	94.2	$ 94.2
Amendment Fee [Member]
Deferred Revenue Arrangement [Line Items]
Total upfront consideration	35
Accelerated Milestone Payment [Member]
Deferred Revenue Arrangement [Line Items]
Total upfront consideration	15
Additional Research Services [Member]
Deferred Revenue Arrangement [Line Items]
Total committed consideration	5.1
ALS Development Services [Member]
Deferred Revenue Arrangement [Line Items]
Total committed consideration	$ 39.1

Related Parties and Related P51

Related Parties and Related Party Transactions - Schedule Represents Allocation of Arrangement Consideration, and Revenue Recognition (Detail) - Astellas [Member] - USD ($) $ in Millions	Jul. 27, 2016	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Allocated Consideration	$ 94.2	$ 94.2
Upfront Revenue Recognition	50	50
Revenue Recognition over Performance Period	44.2	44.2
ALS License [Member]
Deferred Revenue Arrangement [Line Items]
Allocated Consideration	74.9	74.9
Upfront Revenue Recognition	50	50
Revenue Recognition over Performance Period	24.9	24.9
Research and ALS Development Services [Member]
Deferred Revenue Arrangement [Line Items]
Allocated Consideration	$ 19.3	19.3
Upfront Revenue Recognition		0
Revenue Recognition over Performance Period		$ 19.3

Other Research and Developmen52

Other Research and Development Revenue Arrangements Grants - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Aug. 28, 2015
Research and Development Expenses [Line Items]
Grant to support research and development	$ 1,500,000
Milestone payment					$ 500,000
Grant revenue		$ 1,084,000	$ 75,000	$ 75,000
ALSA Grant Revenue [Member]
Research and Development Expenses [Line Items]
Grant revenue		1,084,000	$ 75,000	$ 0
Deferred revenue		$ 0

Other Research and Developmen53

Other Research and Development Revenue Arrangements Grants - Summary of Total Grant Revenues (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total grant revenue	$ 1,084	$ 75	$ 75
ALSA Grant Revenue [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total grant revenue	1,084	75	0
Other Grant Revenue [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total grant revenue	$ 0	$ 0	$ 75

Other Research and Developmen54

Other Research and Development Revenue Arrangements Grants - Summary of Reimbursed Expenses (Detail) - MyoKardia [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development milestone fees	$ 150	$ 0	$ 100
Research and development revenue from Myokardia	$ 150	$ 0	$ 100

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long Term Debt and Unamortized Debt Discount (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Notes payable, gross	$ 30,000	$ 15,000
Less: Unamortized debt discount	(472)	(389)
Accretion of final exit fee	353	28
Carrying value of notes payable	29,881	14,639
Carrying value of notes payable	29,881	14,639
Less: Current portion of long-term debt	(2,500)	0
Long-term debt	$ 27,381	$ 14,639

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail)	Dec. 31, 2016USD ($)shares	Jan. 31, 2017shares	Dec. 31, 2016USD ($)shares	Sep. 30, 2016shares	Feb. 29, 2016USD ($)$ / sharesshares	Oct. 31, 2015USD ($)Installments$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Aug. 31, 2016$ / sharesshares	Jun. 25, 2012shares
Debt Instrument [Line Items]
Warrants outstanding to purchase upon exercise of common stock | shares	4,200,000		4,200,000				4,200,000				7,894,704
Debt instrument, unamortized discount	$ (472,000)		$ (472,000)				$ (472,000)	$ (389,000)
Interest expense							2,698,000	268,000	$ 0
Warrants to Purchase Common Stock [Member]
Debt Instrument [Line Items]
Warrants outstanding to purchase upon exercise of common stock | shares										104,533
Warrants exercise price | $ / shares										$ 5.28
Number of issued shares of common stock related to cashless exercise of warrants | shares			28,569	690,580
Warrants to Purchase Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, unamortized discount	$ 600,000		$ 600,000				$ 600,000
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Warrants outstanding to purchase upon exercise of common stock | shares					68,285	65,189
Warrants exercise price | $ / shares					$ 6.59	$ 6.90
Loan and Security Agreement [Member] | Subsequent Events [Member] | Warrants to Purchase Common Stock [Member]
Debt Instrument [Line Items]
Number of issued shares of common stock related to cashless exercise of warrants | shares		33,368
Cashless exercise of warrants issued | shares		16,126
Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Term loan maximum borrowing capacity						$ 40,000,000
Warrants outstanding to purchase upon exercise of common stock | shares	133,474		133,474			65,189	133,474
Warrants exercise price | $ / shares						$ 6.90
Proceeds from term loan	$ 29,800,000					$ 15,000,000
Remaining term loan borrowing						$ 25,000,000
Debt instrument, installment begin date							2017-10
Interest rate description							The remaining term loans, if drawn, will bear interest at a rate fixed at the time of draw, equal to the greater of (i) 7.50% and (ii) the sum of the three month U.S. LIBOR rate plus 7.31%.
Loan repayment terms							The Company is required to repay the outstanding principal in 36 equal installments beginning October 2017 and is due in full in in October 2020.
Number of installments description							36 equal installments beginning October 2017 and is due in full in in October 2020.
Debt instrument, installment end date							2020-10
Number of installments | Installments						36
Warrant exercisable term							5 years
Warrant expiration condition							The warrants issued in the Loan Agreement became exercisable upon issuance and will remain exercisable for five years from issuance or the closing of a merger consolidation transaction in which the Company is not the surviving entity.
Final payment fee percentage						4.00%
Interest expense							$ 2,700,000	$ 300,000
Effective interest rate on the amounts borrowed under the Agreement	9.30%		9.30%				9.30%	9.30%
Second Term Loan [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Warrants outstanding to purchase upon exercise of common stock | shares					68,285
Warrants exercise price | $ / shares					$ 6.59
Proceeds from term loan					$ 15,000,000
Term loan interest rate						7.50%
Within One Year [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Percentage of prepayment fee						3.00%
Within Two Year [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Percentage of prepayment fee						2.00%
Thereafter [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Percentage of prepayment fee						1.00%
Term Loan Expired on March 2017 [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Remaining term loan borrowing						$ 10,000,000
Term loan interest rate						7.50%
Term Loan Expired on March 2017 [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member] | Three Month U.S. LIBOR [Member]
Debt Instrument [Line Items]
Term loan interest, LIBOR rate						7.31%
Term Loan [Member] | Oxford and Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Term loan interest rate						7.50%

Long-Term Debt - Schedule of Fu

Long-Term Debt - Schedule of Future Minimum Payments under Loan (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total minimum payments	$ 29,881	$ 14,639
Notes payable, gross	30,000	$ 15,000
Loan and Security Agreement [Member] | Oxford and Silicon Valley Bank [Member]
Debt Instrument [Line Items]
2,017	4,768
2,018	11,743
2,019	10,982
2,020	8,938
Total minimum payments	36,431
Less: Interest and final payment	(6,431)
Notes payable, gross	$ 30,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Jun. 07, 2016USD ($)	Feb. 28, 2017USD ($)	Dec. 31, 2016USD ($)Installment	Dec. 31, 2016USD ($)Installment
Other Commitments [Line Items]
Non-cancelable operating lease expiration year				2,018
Non-cancelable operating lease additional extension period				3 years
Settlement agreement amount	$ 4.5
Amgen [Member]
Other Commitments [Line Items]
Co-invest option exercised amount			$ 10	$ 10
Percentage of incremental royalty receivable on annual net sales			1.00%	1.00%
Number of quarterly installments of co-fund payments | Installment			8	8
Co-fund costs requirement value				$ 40
Amgen [Member] | Subsequent Events [Member]
Other Commitments [Line Items]
Co-invest option exercised amount		$ 30
Co-fund costs requirement value		$ 40

Commitments and Contingencies59

Commitments and Contingencies - Rent Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 3,448	$ 3,297	$ 3,338

Commitments and Contingencies60

Commitments and Contingencies - Future Minimum Lease Payments under Noncancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 3,703
2,018	1,860
2,019	0
2,020	0
2,021	0
Thereafter	0
Total	$ 5,563

Commitments and Contingencies61

Commitments and Contingencies - Future Minimum Payments for Co-investment (Detail) - Amgen [Member] $ in Thousands	Dec. 31, 2016USD ($)
Other Commitments [Line Items]
2,017	$ 5,000
2,018	3,750
Total	$ 8,750

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Dec. 31, 2016	Sep. 04, 2015	Jun. 25, 2012	Jan. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Feb. 29, 2016	May 31, 2015	Dec. 31, 2014	Feb. 28, 2014	Jan. 31, 2014	Jun. 30, 2013	Feb. 23, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2014	Aug. 31, 2016	Oct. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized	10,000,000				10,000,000									10,000,000	10,000,000
Preferred stock, shares outstanding	0				0									0	0
Common stock, shares authorized	163,000,000				163,000,000									163,000,000	81,500,000
Common stock, shares outstanding	40,646,595				40,646,595									40,646,595	39,581,692
Convertible preferred stock, issued shares	0				0									0	0
Common stock, shares issued	40,646,595		9,320,176		40,646,595									40,646,595	39,581,692
Per share price of common stock			$ 4.56						$ 8							$ 8	$ 8
Warrants purchase upon exercise of common stock	4,200,000		7,894,704		4,200,000									4,200,000
Aggregate gross proceeds from issuance			$ 60,000,000
Issuance cost of common stock, value			4,000,000													$ 2,800,000
Net proceeds from issue of stock and warrant to public			$ 56,000,000
Number of issued shares of common stock related to exercise of warrants					4,104,966
Aggregate purchase price														$ 0	$ 8,673,000	48,971,000
Allocated stock-based compensation expense														$ 7,146,000	$ 4,567,000	$ 3,330,000
Increased in number of shares of common stock															3,130,000
Stock options granted														1,446,675	1,175,730	944,831
Loan and Security Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants purchase upon exercise of common stock							68,285												65,189
Warrants purchase upon exercise of common stock, exercise price							$ 6.59												$ 6.90
Fair value of common stock							$ 7
Cantor Fitzgerald Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate purchase price	$ 8,900,000
Commission rate														3.00%
Shares issued	808,193
September 2015 Registration Statement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate purchase price														$ 28,700,000
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of options granted														$ 7
Stock options granted															685,000
Performance stock units vested, Number of Shares														0	0	0
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 8,500,000				$ 8,500,000									$ 8,500,000
Weighted-average period														2 years 4 months 24 days
Restricted Stock Units and Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 3,100,000				$ 3,100,000									$ 3,100,000
Weighted-average period														1 year 2 months 12 days
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vested restricted stock units, total fair value														$ 400,000	$ 300,000	$ 100,000
Stock options granted														0	0	0
Performance stock units vested, Number of Shares														45,750	42,078	20,833
Warrants to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants purchase upon exercise of common stock, exercise price			$ 5.28
Warrants to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants purchase upon exercise of common stock																		104,533
Warrants purchase upon exercise of common stock, exercise price																		$ 5.28
Number of issued shares of common stock related to cashless exercise of warrants					28,569	690,580
Warrants to Purchase Common Stock [Member] | Loan and Security Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of warrants							$ 288,000
Contractual term							5 years
Risk-free interest rate							1.70%
Volatility of warrants							75.00%
2004 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grant prices as percentage of the fair market value of the common stock														100.00%
Term to grant nonstatutory stock options and incentive stock options														10 years
Percentage of options grant to new employees														25.00%
Increased in number of shares of common stock								3,130,000						2,000,000
Shares of common stock reserved for issuance	1,588,300				1,588,300									1,588,300
2004 Plan [Member] | New Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting right														Options granted to new employees generally vest 25% after one year and monthly thereafter over a period of four years.
Period from percentage of stock option vested														1 year
Vesting period of options														4 years
2004 Plan [Member] | Existing Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting right														Options granted to existing employees generally vest monthly over a period of four years
Vesting period of options														4 years
Non-employee Stock-Based Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense														$ 147,000	$ 27,000	$ 50,000
Stock options granted														0	0	0
2014 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grant prices as percentage of the fair market value of the common stock											85.00%
Issuance of common stock pursuant to ESPP, shares														129,604	21,167	19,726
Issuance of common stock pursuant to ESPP, per share														$ 7.08	$ 3.24	$ 3.38
2015 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grant prices as percentage of the fair market value of the common stock								85.00%
Shares of common stock reserved for issuance	519,339				519,339									519,339
1997 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Per share price of common stock	$ 12.15				$ 12.15									$ 12.15
Share based compensation, options exercised, total intrinsic value														$ 202,000	$ 94,000	$ 1,000
Weighted-average grant date fair value of options granted														$ 4.77	$ 5.35	$ 6.01
Number of option shares vested														970,241	713,078	601,647
Grant date fair value of option shares vested														$ 4,900,000	$ 3,600,000	$ 3,000,000
MLV [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Convertible preferred stock, issued shares									2,397,278							2,397,278	2,397,278
Net proceeds from sales of common stock																	$ 15,200,000
Underwritten Public Offering [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued										5,031,250
Aggregate purchase price										$ 37,500,000
Gross proceeds from public offerings										$ 40,300,000
At-The-Market Issuance Sales Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum aggregated offer value of saleable and issuable shares		$ 40,000,000
Subsequent Events [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate purchase price													$ 11,000,000
Shares issued													993,408
Subsequent Events [Member] | Warrants to Purchase Common Stock [Member] | Loan and Security Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of issued shares of common stock related to cashless exercise of warrants				33,368
Amgen [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued												1,404,100
Per share price of common stock												$ 7.12
Aggregate purchase price												$ 10,000,000
Common stock fair value														7,500,000
Shares issued												1,404,100
Amgen [Member] | License and Services [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred revenue	$ 2,500,000				$ 2,500,000									$ 2,500,000
Astellas [Member] | Amended Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued									2,040,816							2,040,816	2,040,816
Per share price of common stock									$ 4.90							$ 4.90	$ 4.90
Aggregate purchase price									$ 10,000,000
Series B Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Convertible preferred stock, issued shares			23,026
Issue of series B convertible preferred stock share price			$ 760

Stockholders' Equity - Outstand

Stockholders' Equity - Outstanding Warrants (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Jun. 25, 2012
Class of Stock [Line Items]
Number of Shares	4,200,000	7,894,704
Issued 6/25/2012 [Member]
Class of Stock [Line Items]
Number of Shares	4,104,966
Exercise Price	$ 5.28
Expiration Date	Jun. 25, 2017
Issued 10/19/2015 [Member]
Class of Stock [Line Items]
Number of Shares	65,189
Exercise Price	$ 6.90
Expiration Date	Oct. 19, 2020
Issued 02/10/2016 [Member]
Class of Stock [Line Items]
Number of Shares	68,285
Exercise Price	$ 6.59
Expiration Date	Feb. 10, 2021

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Equity Incentive Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant of Option or Award, Beginning Balance	2,816,010	1,270,478	2,161,829
Shares Available for Grant of Option or Award, Increase in authorized shares		3,130,000
Shares Available for Grant of Option or Award, Options granted	(1,446,675)	(1,175,730)	(944,831)
Shares Available for Grant of Option or Award, Options exercised	0	0	0
Shares Available for Grant of Option or Award, Options forfeited/expired	257,465	326,762	95,980
Shares Available for Grant of Option or Award, Ending Balance	1,588,300	2,816,010	1,270,478
Stock Options Outstanding, Beginning Balance	4,078,159	3,297,826	2,449,365
Stock Options Outstanding, Options granted	1,446,675	1,175,730	944,831
Stock Options Outstanding, Options forfeited/expired	(257,465)	(326,762)	(95,980)
Shares Available for Grant of Options or Awards, Restricted stock units forfeited		0
Stock Options Outstanding, Ending Balance	5,192,813	4,078,159	3,297,826
Weighted Average Exercise Price per Share - Stock Options, Beginning Balance	$ 10.94	$ 12.62	$ 15.15
Stock Options Outstanding, Exercisable	3,364,286
Weighted Average Exercise Price per Share - Stock Options, Options granted	$ 7.10	7.62	8.80
Stock Options Outstanding, Vested and expected to vest	5,147,387
Weighted Average Exercise Price per Share - Stock Options, Options exercised	$ 6.75	6.22	6
Weighted Average Exercise Price per Share - Stock Options, Options forfeited/expired	24.25	16.83	39.74
Weighted Average Exercise Price per Share - Stock Options, Ending Balance	9.27	$ 10.94	$ 12.62
Weighted Average Exercise Price per Share - Stock Options, Exercisable	10.24
Weighted Average Exercise Price per Share - Stock Options, Vested and expected to vest, Outstanding	$ 9.29
Weighted Average Remaining Contractual Life	6 years 9 months 29 days
Weighted Average Remaining Contractual Life, Exercisable at December 31, 2016	5 years 9 months 29 days
Weighted Average Remaining Contractual Life, Vested and expected to vest as of December 31, 2016	6 years 9 months 22 days
Aggregate Intrinsic Value	$ 21,294
Aggregate Intrinsic Value, Exercisable at December 31, 2016	12,771
Aggregate Intrinsic Value, Vested and expected to vest as of December 31, 2016	$ 21,075
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding, Options exercised	(74,556)	(68,635)	(390)
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant of Option or Award, Restricted stock units granted	(47,000)	(739,000)	(43,500)
Shares Available for Grant of Option or Award, Restricted stock units forfeited	8,500	3,500	1,000
Shares Available for Grant of Option or Award, Options granted	0	0	0
Shares Available for Grant of Option or Award, Options forfeited/expired	8,500
Shares Available for Grant of Options or Awards, Restricted stock units forfeited	0		0
Weighted Average Exercise Price per Share - Stock Options, Restricted stock units granted	$ 0	$ 0	$ 0
Weighted Average Exercise Price per Share - Stock Options, Restricted stock units forfeited	$ 0	$ 0	$ 0

Stockholders' Equity - Summar65

Stockholders' Equity - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units outstanding, Number of Shares, Beginning Balance	71,752	63,330	41,663
Restricted stock units granted, Number of Shares	47,000	739,000	43,500
Restricted stock units vested, Number of Shares	(45,750)	(42,078)	(20,833)
Restricted stock units forfeited, Number of Shares	(8,500)	(3,500)	(1,000)
Unvested restricted stock units outstanding, Number of Shares, Ending Balance	64,502	71,752	63,330
Restricted stock units outstanding, Weighted Average Award Date Fair Value per Share, Beginning Balance	$ 8.49	$ 8.51	$ 6
Restricted stock units granted, Weighted Average Award Date Fair Value per Share	6.67	7.96	9.65
Restricted stock units vested, Weighted Average Award Date Fair Value per Share	8.69	7.82	6
Restricted stock units forfeited, Weighted Average Award Date Fair Value per Share	7.20	8.68	6
Unvested restricted stock units outstanding, Weighted Average Award Date Fair Value per Share, Ending Balance	$ 7.19	$ 8.49	$ 8.51

Stockholders' Equity - Summar66

Stockholders' Equity - Summary of Performance Stock Unit Activity (Detail) - Performance Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units outstanding, Number of Shares, Beginning Balance	685,000	0
Restricted stock units granted, Number of Shares	0	685,000
Restricted stock units vested, Number of Shares	0	0	0
Restricted stock units forfeited, Number of Shares	0	0
Unvested restricted stock units outstanding, Number of Shares, Ending Balance	685,000	685,000	0
Restricted stock units outstanding, Weighted Average Award Date Fair Value per Share, Beginning Balance	$ 7	$ 0
Performance stock units granted, Weighted Average Award Date Fair Value per Share	0	7
Restricted stock units vested, Weighted Average Award Date Fair Value per Share	0	0
Restricted stock units forfeited, Weighted Average Award Date Fair Value per Share	0	0
Unvested restricted stock units outstanding, Weighted Average Award Date Fair Value per Share, Ending Balance	$ 7	$ 7	$ 0

Stockholders' Equity - Stock-Ba

Stockholders' Equity - Stock-Based Compensation Related to Stock Options, Restricted Stock Awards, Restricted Stock Unit, and Employee Stock Purchases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 7,146	$ 4,567	$ 3,330
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	4,252	1,828	1,361
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,894	$ 2,739	$ 1,969

Stockholders' Equity - Fair Val

Stockholders' Equity - Fair Value of Share-Based Payments was Estimated on Date of Grant Using Black-Scholes Option Pricing Model Based on Weighted Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ESPP [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Risk-free interest rate	0.50%	0.30%	0.20%
Volatility	74.00%	75.30%	86.00%
Expected term in years	6 months	6 months 22 days	1 year 3 months
Expected dividend yield	0.00%	0.00%	0.00%
Options [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Risk-free interest rate	1.90%	1.70%	1.90%
Volatility	74.00%	79.40%	77.10%
Expected term in years	6 years 5 months 9 days	6 years 4 months 17 days	6 years 3 months 18 days
Expected dividend yield	0.00%	0.00%	0.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Provision for income tax	$ 0	$ 0	$ 0
Increase (decrease) in valuation allowance	(2,200,000)	13,900,000	1,000,000
Net operating loss related to tax stock option deductions	$ 2,000,000
Research and development credits and orphan drug credits, federal carryforwards will expire	2,021
Percentage of income tax likely to be realized	50.00%
Unrecognized tax benefits	$ 6,300,000	5,500,000	5,100,000
Unrecognized tax benefits not accrue any penalties	0	$ 0	$ 0
Federal Tax [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 388,100,000
Net operating loss carryforwards expiration	2,020
Credit carryforwards for federal and state	$ 44,400,000
Federal and State Tax [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 249,900,000
Net operating loss carryforwards expiration	2,017
Credit carryforwards for federal and state	$ 13,600,000

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income (Loss) Before Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
United States	$ 16,453	$ (37,501)	$ (14,646)
Foreign	0	0	0
Income (loss) before income taxes	$ 16,453	$ (37,501)	$ (14,646)

Income Taxes - Company Recorded

Income Taxes - Company Recorded Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal	$ 0	$ 0	$ 0
State	0	0	0
Total	0	0	0
Deferred:
Federal	0	0	0
State	0	0	0
Total	$ 0	$ 0	$ 0

Income Taxes - Company's Deferr

Income Taxes - Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Depreciation and amortization	$ 766	$ 769	$ 780
Capitalized R&D	11,675	13,150	15,176
Reserves and accruals	10,258	12,899	6,217
Net operating losses	146,961	153,251	148,184
Tax credits	46,998	38,742	34,543
Total deferred tax assets	216,658	218,811	204,900
Less: Valuation allowance	(216,658)	(218,811)	(204,900)
Net deferred tax assets	$ 0	$ 0	$ 0

Income Taxes - Company's Valuat

Income Taxes - Company's Valuation and Qualifying Accounts (Detail) - Deferred Tax Valuation Allowance [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 218,811	$ 204,900	$ 203,863
Charged to Expenses	(2,153)	13,911	1,037
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	$ 216,658	$ 218,811	$ 204,900

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax at federal statutory tax rate	34.00%	(34.00%)	(34.00%)
State income tax, net of federal tax benefit	2.00%	0.00%	(1.00%)
State Apportionment	(7.00%)	0.00%	28.00%
Tax credits (net)	(32.00%)	(7.00%)	(7.00%)
Deferred tax assets (utilized) not benefited	(15.00%)	37.00%	7.00%
Stock-based compensation	7.00%	2.00%	5.00%
NOL Expiration	9.00%	2.00%	2.00%
Other	2.00%	0.00%	0.00%
Total	0.00%	0.00%	0.00%

Income Taxes - Schedule of Acti

Income Taxes - Schedule of Activity Related to our Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at the beginning of the year	$ 6,715	$ 6,274
Decrease related to prior year tax positions	5	0
Increase related to current year tax positions	845	441
Balance at the end of the year	$ 7,565	$ 6,715

Quarterly Financial Data - Summ

Quarterly Financial Data - Summary of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 33,138	$ 59,047	$ 5,802	$ 8,421	$ 9,757	$ 7,945	$ 6,542	$ 4,414
Net income (loss)	$ 7,157	$ 33,362	$ (11,611)	$ (12,455)	$ (9,229)	$ (8,849)	$ (10,551)	$ (8,872)	$ 16,453	$ (37,501)	$ (14,646)
Net income (loss) per share - basic	$ 0.18	$ 0.84	$ (0.29)	$ (0.31)					$ 0.41	$ (0.97)	$ (0.41)
Net (loss) per share - basic and diluted					$ (0.24)	$ (0.23)	$ (0.27)	$ (0.23)
Net income (loss) per share -diluted	$ 0.16	$ 0.77	$ (0.29)	$ (0.31)					$ 0.39	$ (0.97)	$ (0.41)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Feb. 01, 2017	Feb. 28, 2017	Feb. 23, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 25, 2012
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Weighted average sale price						$ 8	$ 4.56
Net proceeds of issuance of common stock				$ 0	$ 8,673	$ 48,971
Subsequent Events [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Common stock, shares issued in period			993,408
Net proceeds of issuance of common stock			$ 11,000
Subsequent Events [Member] | CE Offering [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Common stock, shares issued in period			185,215
Weighted average sale price			$ 11.24
Net proceeds of issuance of common stock			$ 2,100
Subsequent Events [Member] | Royalty Purchase Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percentage of royalty	4.50%
Cash payment under Royalty Agreement	$ 90,000
Value of common stock purchased under Royalty Agreement	$ 10,000
Royalty rate increase percentage	1.00%
Subsequent Events [Member] | Amgen [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Co-invest option exercised amount		$ 30,000
Co-fund costs requirement value		$ 40,000
Percentage of incremental royalty receivable on annual net sales		4.00%