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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	May 04, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	CYTK
Entity Registrant Name	CYTOKINETICS INC
Entity Central Index Key	0001061983
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity File Number	000-50633
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3291317
Entity Address, Address Line One	280 East Grand Avenue
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	624-3000
Entity Common Stock, Shares Outstanding		59,469,525
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 49,776	$ 36,433
Short-term investments	170,930	188,679
Accounts receivable	2,704	5,163
Prepaid expenses and other current assets	2,528	3,477
Total current assets	225,938	233,752
Long-term investments	16,510	42,650
Property and equipment, net	5,162	4,530
Operating lease right-of-use assets and other assets	8,972	8,882
Total assets	256,582	289,814
Current liabilities:
Accounts payable	3,527	8,160
Accrued liabilities	9,677	12,123
Short-term lease liability	5,030	4,616
Other current liabilities	2,507	1,124
Total current liabilities	20,741	26,023
Term loan, net	45,340	45,052
Convertible notes, net	85,455	84,205
Liability related to the sale of future royalties, net	148,983	143,276
Long-term lease liability	1,774	2,195
Total liabilities	302,293	300,751
Commitments and contingencies	0	0
Stockholders’ deficit:
Preferred stock, $0.001 par value	0	0
Common stock, $0.001 par value	59	59
Additional paid-in capital	857,038	853,341
Accumulated other comprehensive income	1,613	679
Accumulated deficit	(904,421)	(865,016)
Total stockholders’ deficit	(45,711)	(10,937)
Total liabilities and stockholders’ deficit	$ 256,582	$ 289,814

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Total revenues	$ 3,825	$ 8,464
Operating expenses:
Research and development	21,738	23,545
General and administrative	12,449	9,437
Total operating expenses	34,187	32,982
Operating loss	(30,362)	(24,518)
Interest expense	(4,077)	(1,170)
Non-cash interest expense on liability related to the sale of future royalties	(5,689)	(4,819)
Interest and other income, net	723	1,141
Net loss	$ (39,405)	$ (29,366)
Net loss per share — basic and diluted	$ (0.66)	$ (0.54)
Weighted-average number of shares used in computing net loss per share — basic and diluted	59,270	54,821
Other comprehensive income:
Unrealized gain on available-for-sale securities, net	$ 934	$ 106
Comprehensive loss	(38,471)	(29,260)
Research and Development Revenues [Member]
Revenues:
Total revenues	$ 3,825	$ 8,464

Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2018	$ 25,934	$ 55	$ 768,703	$ 500	$ (743,324)
Beginning Balance, shares at Dec. 31, 2018		54,717,906
Exercise of stock options, value	31	$ 0	31	0	0
Exercise of stock options, shares		5,116
Vesting of restricted stock units, net of taxes withheld, value	(732)	$ 0	(732)	0	0
Vesting of restricted stock units, net of taxes withheld, shares		165,347
Stock-based compensation	2,282	$ 0	2,282	0	0
Issuance of common stock under at-the-market offering, net of issuance costs	5,117	$ 0	5,117	0	0
Issuance of common stock under at-the-market offering, net of issuance costs, shares		562,811
Other comprehensive income	106	$ 0	0	106	0
Net loss	(29,366)	0	0	0	(29,366)
Ending Balance at Mar. 31, 2019	3,372	$ 55	775,401	606	(772,690)
Ending Balance, shares at Mar. 31, 2019		55,451,180
Beginning Balance at Dec. 31, 2019	(10,937)	$ 59	853,341	679	(865,016)
Beginning Balance, shares at Dec. 31, 2019		59,172,124
Exercise of stock options, value	93	$ 0	93	0	0
Exercise of stock options, shares		12,165
Vesting of restricted stock units, net of taxes withheld, value	(2,255)	$ 0	(2,255)	0	0
Vesting of restricted stock units, net of taxes withheld, shares		274,563
Stock-based compensation	3,524	$ 0	3,524	0	0
Claims settlement under Section 16(b)	2,151	0	2,151	0	0
Issuance of warrants	184	0	184	0	0
Other comprehensive income	934	0	0	934	0
Net loss	(39,405)	0	0	0	(39,405)
Ending Balance at Mar. 31, 2020	$ (45,711)	$ 59	$ 857,038	$ 1,613	$ (904,421)
Ending Balance, shares at Mar. 31, 2020		59,458,852

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (39,405)	$ (29,366)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense on liability related to sale of future royalties	5,706	4,819
Non-cash stock-based compensation expense	3,524	2,282
Depreciation and amortization of property and equipment	408	286
Interest receivable and amortization on investments	293	(533)
Non-cash interest expense related to debt	1,724	183
Changes in operating assets and liabilities:
Accounts receivable	2,459	(1,934)
Contract assets	0	2,082
Prepaid and other assets	949	(983)
Operating lease right-of-use assets	1,016	856
Accounts payable	(4,633)	(1,217)
Accrued and other liabilities	(1,064)	(2,466)
Operating lease liabilities	(1,112)	(916)
Net cash used in operating activities	(30,135)	(26,907)
Cash flows from investing activities:
Purchases of investments	(10,592)	(41,295)
Sales and maturities of investments	55,122	61,196
Purchases of property and equipment	(1,041)	(257)
Net cash provided by investing activities	43,489	19,644
Cash flows from financing activities:
Proceeds from and payments for stock based award activities, net	(2,162)	(701)
Claims settlement under Section 16(b)	2,151	0
Issuance of common stock under at-the-market offering, net of issuance costs	0	5,117
Net cash (used in) provided by financing activities	(11)	4,416
Net increase (decrease) in cash and cash equivalents	13,343	(2,847)
Cash and cash equivalents, beginning of period	36,433	42,256
Cash and cash equivalents, end of period	49,776	39,409
Non-cash investing and financing activities:
Right-of-use assets recognized in exchange for lease obligations	$ 1,106	$ 10,686

Organization and Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Significant Accounting Policies

Note 1 — Organization and Significant Accounting Policies

Cytokinetics, Incorporated (the “Company”, “we” or “our”) was incorporated under the laws of the state of Delaware on August 5, 1997. The Company is a late stage biopharmaceutical company focused on the discovery and development of novel small molecule therapeutics that modulate muscle function for the potential treatment of serious diseases and medical conditions.

Our financial statements contemplate the conduct of our operations in the normal course of business. We have incurred an accumulated deficit of $904.4 million since inception and there can be no assurance that we will attain profitability. The Company anticipates that it will have operating losses and net cash outflows in future periods.

We are subject to risks common to late stage biopharmaceutical companies including, but not limited to, development of new drug candidates, dependence on key personnel, and the ability to obtain additional capital as needed to fund our future plans. Our liquidity will be impaired if sufficient additional capital is not available on terms acceptable to us. To date, we have funded operations primarily through sales of our common stock, contract payments under our collaboration agreements, sale of future royalties, debt financing arrangements and issuances, government grants and interest income. Until we achieve profitable operations, we intend to continue to fund operations through payments from strategic collaborations, additional sales of equity and debt securities, grants and debt financings. We have never generated revenues from commercial sales of our drugs and may not have drugs to market for at least several years, if ever. Our success is dependent on our ability to enter into new strategic collaborations and/or raise additional capital and to successfully develop and market one or more of our drug candidates. As a result, we may choose to raise additional capital through equity or debt financings to continue to fund operations in the future. We cannot be certain that sufficient funds will be available from such a financing or through a collaborator when required or on satisfactory terms. Additionally, there can be no assurance that our drug candidates will be accepted in the marketplace or that any future products can be developed or manufactured at an acceptable cost. These factors could have a material adverse effect on our future financial results, financial position and cash flows.

Based on the current status of our research and development activities, we believe that our existing cash, cash equivalents and investments will be sufficient to fund cash requirements for at least the next 12 months from the filing date of this Quarterly Report on Form 10-Q. If, at any time, our prospects for financing research and development programs decline, we may decide to reduce research and development expenses by delaying, discontinuing or reducing funding of one or more of our research or development programs. Alternatively, we might raise funds through strategic collaborations, public or private financings or other arrangements. Such funding, if needed, may not be available on favorable terms, or at all. These financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Basis of Presentation

Our condensed consolidated financial statements include the accounts of Cytokinetics and our wholly-owned subsidiary. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. The financial statements include all adjustments (consisting only of normal recurring adjustments) that management believes are necessary for the fair statement of our financial information. These interim results are not necessarily indicative of results to be expected for the full fiscal year or any future interim period. The balance sheet as of December 31, 2019 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. The financial statements and related disclosures have been prepared with the presumption that users of the interim financial statements have read or have access to the audited financial statements for the preceding fiscal year. Accordingly, these financial statements should be read in conjunction with the audited financial statements and notes thereto contained in the Company’s Form 10-K for the year ended December 31, 2019, as filed with the Securities and Exchange Commission.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the condensed consolidated financial statements and reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, investments, accrued research and development expenses, other long-lived assets, stock-based compensation, operating lease assets and liabilities, and the valuation of deferred tax assets. We base our estimates on our historical experience and also on assumptions that we believe are reasonable; however, actual results could significantly differ from those estimates.

Recent Accounting Pronouncements

In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-13, ‘Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. ASU 2016-13 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. ASU 2016-13 is effective for annual and interim reporting periods beginning after December 15, 2019. We adopted ASU 2016-13 as of January 1, 2020 and the adoption did not have a material impact on the Condensed Consolidated Financial Statements.

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (“ASU 2018-18”), which makes targeted improvements to clarify the interaction between Topic 808, Collaborative Arrangements, and Topic 606, Revenue from Contracts with Customers. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. We adopted ASU 2018-18 on January 1, 2020 and the adoption did not have a material impact on the Condensed Consolidated Financial Statements.

In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04’). ASU 2020-04 provides optional guidance for a limited period of time to ease the potential burden associated with the expected market transition from the London Inter-Bank Offer Rate ("LIBOR") to alternative reference rates. Companies can apply ASU 2020-04 immediately, however the guidance will only be available until December 31, 2022. The Company’s term loan utilizes LIBOR as the reference rate and the Company is currently evaluating the impact that adopting this new accounting standard will have on our Condensed Consolidated Financial Statements and related disclosures.

Research and Development Arrangements

3 Months Ended

Mar. 31, 2020

Research And Development [Abstract]

Research and Development Arrangements

Note 3 — Research and Development Arrangements

Amgen Inc. (“Amgen”)

We and Amgen continue activities related to novel small molecule therapeutics, including omecamtiv mecarbil, that activate cardiac muscle contractility for potential applications in the treatment of heart failure under the collaboration and option agreement between the Company and Amgen dated December 29, 2006, as amended (the “Amgen Agreement”).

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

In 2018, we paid Amgen $18.8 million and completed the exercise of our option under the Amgen Agreement to co-invest $40.0 million in the Phase 3 development program of omecamtiv mecarbil in exchange for a total incremental royalty from Amgen of up to 4% on increasing worldwide sales of omecamtiv mecarbil outside Japan (the “Co-Invest Option”).

We recognize research and development revenue for reimbursements from Amgen of both internal costs of certain full-time employee equivalents and other costs related to the Amgen Agreement. Research and development revenue from Amgen of $2.3 million and $4.2 million in the first quarters of 2020 and 2019, respectively, consists of reimbursement of costs we incurred related to METEORIC-HF (Multicenter Exercise Tolerance Evaluation of Omecamtiv Mecarbil Related to Increased Contractility in Heart Failure), a Phase 3 clinical trial intended to evaluate the potential of omecamtiv mecarbil to increase exercise performance.

We had accounts receivable of $2.3 million from Amgen as of March 31, 2020 and $3.3 million as of December 31, 2019.

Astellas Pharma Inc. (“Astellas”)

We and Astellas entered into that certain License and Collaboration Agreement, dated June 21, 2013 (as subsequently amended and restated, the “Astellas Agreement”) focused on the research, development, and commercialization of skeletal muscle activators.

In 2014, we and Astellas amended and restated the Astellas Agreement and expanded the objective of the collaboration to include spinal muscular atrophy (“SMA”) and potentially other neuromuscular indications for reldesemtiv and other fast skeletal muscle troponin activators (“FSTAs”).

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

On April 23, 2020, we and Astellas entered into the two agreements referenced below which, taken together, amend and restate the Company’s research, development and commercialization collaboration with Astellas under the Astellas Agreement.

Fast Skeletal Regulatory Activator Agreement

The Company and Astellas entered into that certain Fast Skeletal Regulatory Activator Agreement, dated April 23, 2020 (the “Astellas FSRA Agreement”). As a result of the Astellas FSRA Agreement, the Company will now have exclusive control and responsibility for the Company's future development and commercialization of reldesemtiv, CK-601 and other fast skeletal regulatory activator (collectively “FSRA”) compounds and products, and accordingly, Astellas has agreed to terminate its license to all FSRA compounds and related products.

Under the Astellas FSRA Agreement, Astellas has agreed to pay one-third of the out-of-pocket clinical development costs which may be incurred in connection with the Company’s potential Phase 3 clinical trial of reldesemtiv in ALS, up to a maximum contribution by Astellas of $12 million. In addition, Astellas has agreed to non-cash contributions to the Company, which include the transfer of its existing inventories of active pharmaceutical ingredient of reldesemtiv and CK-601. Astellas has also agreed to the continued conduct of ongoing stability studies pertaining to such existing inventories of active pharmaceutical ingredient, at Astellas’ cost. In exchange, the Company will pay Astellas a low- to mid- single digit royalty on sales of reldesemtiv in the United States, Canada, United Kingdom and the European Union until the later of (i) ten years following the first commercial sale of such product in a major market country, or (ii) December 31, 2034, subject to certain royalty reduction provisions. The Company would not owe Astellas royalties on sales of reldesemtiv in any other country, or on the sale of any FSRA compounds or related products other than reldesemtiv.

License and Collaboration Agreement for Other Skeletal Sarcomere Activators

The Company and Astellas also entered into that certain License and Collaboration Agreement for Other Skeletal Sarcomere Activators, dated April 23, 2020 (the “Astellas OSSA Agreement”), which is an amendment and restatement of the Astellas Agreement and removes the FSRA compounds and related products from the collaboration.

Under the Astellas OSSA Agreement, additional research and early and late state development milestone payments for research and clinical milestones, including the initiation of certain clinical studies, the submission of an application for marketing authorization for a drug candidate to certain regulatory authorities and the commercial launch of collaboration products could total up to $250.0 million, except under certain scenarios. Additionally, $200.0 million in commercial milestones could be received under the Astellas OSSA Agreement provided certain sales targets are met. We are eligible to receive $1.0 million in research milestone payments under the collaboration for each future potential drug candidate. Due to the nature of drug development, including the inherent risk of development and approval of drug candidates by regulatory authorities, it is not possible to estimate if and when these milestone payments could be achieved or become due.

We continue to recognize research revenue for reimbursements from Astellas of internal costs of certain full-time employee equivalents, supporting collaborative research and development programs, and of other costs related to those programs. Research and development revenue from Astellas was $1.5 million and $4.3 million in the first quarters of 2020 and 2019, respectively.

We had no accounts receivable from Astellas as of March 31, 2020 and $1.9 million as of December 31, 2019.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

Note 4 — Fair Value Measurements

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

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

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

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

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

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

Fair value of financial assets:

The follow tables set forth the fair value of our financial assets, which consists of cash equivalents and investments classified as available-for-sale securities, that were measured on a recurring basis (in thousands):

		March 31, 2020
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	Level 1	$	46,538	$	—	$	—		$	46,538
U.S. Treasury securities	Level 1		115,391		1,047		—			116,438
Agency bonds	Level 2		28,391		83		—			28,474
Commercial paper	Level 2		6,227		5		—			6,232
Corporate obligations	Level 2		35,754		8		(103	)		35,659
		$	232,301	$	1,143	$	(103	)	$	233,341

		December 31, 2019
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	Level 1	$	31,535	$	—	$	—		$	31,535
U.S. Treasury securities	Level 1		134,845		72		(1	)		134,916
Agency bonds	Level 2		47,024		23		(9	)		47,038
Commercial paper	Level 2		10,435		4		—			10,439
Corporate obligations	Level 2		40,426		24		(7	)		40,443
		$	264,265	$	123	$	(17	)	$	264,371

Interest income, net was $0.7 million and $1.1 million in the first quarters of 2020 and 2019, respectively.

Investments available for sale as of March 31, 2020 and December 31, 2019 exclude an investment in equity classified as a Level 1 investment in our short-term investments with a fair value of $0.6 million and $1.0 million, respectively. In the first quarters of 2020 and 2019, we recognized an unrealized loss of $0.4 million and an immaterial unrealized gain, respectively. As of March 31, 2020, unrealized losses were not due to changes in credit risk and we believe investments with an unrealized loss would be held until maturity.

No credit losses on debt securities were recorded during the three-month periods ended March 31, 2020 and March 31, 2019. In its evaluation to determine expected credit losses, management considered all available historical and current information, expectations of future economic conditions, the type of security, the credit rating of the security, and the size of the loss position, as well as other relevant information. The Company does not intend to sell, and is unlikely to be required to sell, any of these available-for-sale investments before their effective maturity or market price recovery.

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

Fair value of financial liabilities:

As of March 31, 2020, the fair value of our term loan approximated its carrying value of $45.3 million, because it is carried at a market observable interest rate, which is a Level 2 input (see Note 7 – “Debt”).

As of March 31, 2020, the estimated fair value of our convertible notes was $181.5 million and was based upon observable, Level 2 inputs, including pricing information from recent trades of the convertible notes (see Note 7 – “Debt”).

As of March 31, 2020, the fair value of the liability related to the sale of future royalties is based on our current estimates of future royalties expected to be paid to RPI Finance Trust (“RPI”), an entity related to Royalty Pharma, over the life of the arrangement, which are considered Level 3 inputs (See Note 8 – “Liability Related to Sale of Future Royalties”).

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

- Definition

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

+ References + Details

Debt

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Debt

Note 7 — Debt

Term Loan

Prior to May 17, 2019 we maintained a loan and security agreement dated as of October 19, 2015, as amended (the “Original Loan Agreement”) with Oxford Finance LLC (“Oxford”) and Silicon Valley Bank (“SVB”) (Oxford and SVB, collectively the “Lenders”) to fund our working capital and other general corporate needs.

Subsequently, we and the Lenders entered into that certain Loan and Security Agreement, dated May 17, 2019, as amended, (the “Term Loan Agreement”) pursuant to which the Lenders made available to us a $45.0 million loan (the “Term Loan”). The proceeds of the Term Loan were used in part to repay in full all amounts outstanding under the Original Loan Agreement, an aggregate principal amount of $42.0 million.

The Term Loan was accounted for as a debt modification in a non-troubled debt restructuring, rather than a debt extinguishment, based on a comparison of the present value of the cash flows under the terms of the debt immediately before and after the effective date of the Term Loan, which resulted in a change of less than 10%. As a result, issuance costs paid to the Lenders in connection with the Term Loan were recorded as a reduction of the carrying amount of the debt liability and were not significant. Unamortized issuance costs as of the date of the modification were amortized to interest expense over the repayment term of Term Loan.

Both borrowings under the Original Loan Agreement and Term Loan Agreement bear interest at an annual rate equal to the greater of (a) 8.05% or (b) the sum of 6.81% plus the 30-day U.S. LIBOR rate. The borrowing under the Original Loan Agreement was repayable in monthly interest-only payments through November 2019 followed by 35 months of monthly payments of interest and principal. The borrowing under the Term Loan Agreement was initially repayable in monthly interest-only payments through December 31, 2020. The interest-only period was automatically extended until July 1, 2021 as a result of the Company’s initiation of a Phase 2 trial for CK-274 in cardiomyopathy and could potentially be extended through December 31, 2021 if positive results are achieved in the Phase 3 GALACTIC-HF trial for omecamtiv mecarbil in chronic heart failure, in form and content reasonably acceptable to the Lenders. The ultimate interest-only period will be followed by equal monthly payments of principal and interest to the maturity date in December 2023. We are required to make a final payment upon loan maturity of 6.00% of the notes payable, which we accrete over the life of the Term Loan. Our obligations under the Term Loan Agreement are secured by substantially all our current and future assets, other than our intellectual property.

Interest expense for the Term Loan for the first quarters of 2020 and 2019 was $1.2 million and $1.2 million, respectively. As of March 31, 2020, the interest rate applicable to borrowings under the Term Loan was 8.05%.

The Term Loan Agreement contains customary representations and warranties and customary affirmative and negative covenants applicable to us and includes customary events of default, including but not limited to the nonpayment of principal or interest, violations of covenants and material adverse changes. Upon an event of default, the Lenders may, among other things, accelerate the loans and foreclose on the collateral. Our obligations under the Term Loan Agreement are secured by substantially all our current and future assets, other than our intellectual property. If the Term Loan becomes subject to mandatory prepayment under these provisions, we are subject to certain prepayment premiums of 3.00% in the first year, 2.00% in the second year and 1.00% in the third year and thereafter. We determined that these contingent prepayment provisions were an embedded component that qualified as a derivative which should be bifurcated from the Term Loan and accounted for separately from the host contract. As of March 31, 2020, the fair value of this embedded derivative was immaterial.

Future minimum payments under the Term Loan Agreement are (in thousands):

Years ending December 31:
2020 remainder	$	2,785
2021		12,519
2022		20,264
2023		23,381
Future minimum payments		58,949
Less: Interest and final payment		(13,949	)
Term Loan, gross	$	45,000

Convertible Notes

On November 13, 2019, the Company issued $138.0 million aggregate principal amount of 2026 Notes. The 2026 Notes are unsecured obligations and bear interest at an annual rate of 4.0% per year, payable semi-annually on May 15 and December 15 of each year, beginning May 15, 2020. The 2026 Notes are governed by an indenture between the Company and U.S. Bank National Association, as trustee. The 2026 Notes will mature on November 15, 2026, unless earlier repurchased or redeemed by the Company or converted at the option of the holders. The Company may redeem the 2026 Notes prior to the maturity date but is not required to and no sinking fund is provided for the 2026 Notes. The 2026 Notes may be converted, under certain circumstances as described below, based on an initial conversion rate of 94.7811 shares of common stock per $1,000 principal amount (which represents an initial conversion price of $10.55 per share). The conversion rate for the 2026 Notes will be subject to adjustment upon the occurrence of certain specified events. In addition, upon the occurrence of a make-whole fundamental change (as defined in the indenture), the Company will, in certain circumstances, increase the conversion rate by a number of additional shares for a holder that elects to convert its notes in connection with such make-whole fundamental change. The Company received approximately $133.9 million in net proceeds, after deducting the initial purchasers’ discount, from the issuance of the 2026 Notes.

The 2026 Notes may be converted at the option of the holder under any of the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on March 31, 2020 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter exceeds 127.5% of the last reported sale price of the Company’s common stock on November 7, 2019; (2) during the 5 consecutive business days immediately after any 10 consecutive trading day period (such 10 consecutive trading day period, the “measurement period”) if the trading price per $1,000 principal amount of 2026 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price per share of the Company’s common stock on such trading day and the conversion rate on such trading day; (3) upon the occurrence of certain corporate events or distributions on the Company’s common stock; (4) if the Company calls the 2026 Notes for redemption; and (5) at any time from, and including, July 15, 2026 until the close of business on the scheduled trading day immediately before the maturity date, November 15, 2026. The Company will settle conversions by paying or delivering, as applicable, cash, shares of the Company’s common stock, or a combination of cash and shares of the Company’s common stock, at the Company’s election, based on the applicable conversion rate.

The 2026 Notes will be redeemable, in whole or in part, at the Company’s option at any time, and from time to time, on or after November 20, 2023 and, in the case of any partial redemption, on or before the 60th scheduled trading day before the maturity date, at a cash redemption price equal to the principal amount of the 2026 Notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date but only if the last reported sale price per share of the Company’s common stock exceeds 130% of the conversion price on (1) each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the trading day immediately before the date the Company sends the related redemption notice; and (2) the trading day immediately before the date the Company sends such notice. If a “fundamental change” (as defined in the indenture) occurs, then, subject to certain exceptions, holders may require the Company to repurchase their 2026 Notes at a cash repurchase price equal to the principal amount of the 2026 Notes to be repurchased, plus accrued and unpaid interest, if any, to, but excluding, the fundamental change repurchase date.

In accounting for the issuance of the 2026 Notes, the Company separated the 2026 Notes into liability and equity components. The carrying amount of the liability component of approximately $84.2 million was calculated by using a discount rate of 12.0%, which was estimated to be the Company’s borrowing rate on the date of the issuance of the notes for a similar debt instrument without the conversion feature. The carrying amount of the equity component of approximately $49.5 million, representing the conversion option, was determined by deducting the fair value of the liability component from the par value of the 2026 Notes. The equity component of the 2026 Notes is included in additional paid-in capital in the consolidated balance sheets and is not remeasured as long as it continues to meet the conditions for equity classification. The difference between the principal amount of the 2026 Notes and the liability component (the “debt discount”) is amortized to interest expense using the effective interest method over the term of the 2026 Notes.

Debt issuance costs for the issuance of the 2026 Notes were approximately $5.0 million, consisting of initial purchasers' discount and other issuance costs. In accounting for the transaction costs, the Company allocated the total amount incurred to the liability and equity components using the same proportions as the proceeds from the 2026 Notes. Transaction costs attributable to the liability component were approximately $3.1 million, were recorded as debt issuance cost (presented as contra debt in the consolidated balance sheet) and are being amortized to interest expense over the term of the 2026 Notes. The transaction costs attributable to the equity component were approximately $1.9 million and were netted with the equity component in stockholders’ equity. As of March 31, 2020, the unamortized debt issuance cost for the 2026 Notes was $3.0 million on the consolidated balance sheet.

The following table presents the total amount of interest cost recognized relating to the 2026 Notes (in thousands):

	Three Months Ended March 31, 2020
Contractual interest expense	$	1,380
Amortization of debt discount		1,237
Amortization of debt issuance costs		12
Total interest costs recognized	$	2,629

The effective interest rate on the liability component of the 2026 Notes was 12.5% for the year ended March 31, 2020, which remains unchanged from the date of issuance. The remaining unamortized debt discount was $49.5 million as of March 31, 2020, and will be amortized over approximately 6.7 years. The if-converted value of the 2026 Notes exceeded its principal amount by $58.6 million as of March 31, 2020.

Capped Call Transactions

In connection with the offering of the 2026 Notes, the Company entered into privately-negotiated capped call transactions with one of the underwriters in the offering or its affiliate. The Company used approximately $13.4 million of the net proceeds from the offering of the 2026 Notes to pay the cost of the capped call transactions. The capped call transactions are expected generally to reduce potential dilution to the Company’s common stock upon any conversion of the 2026 Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of converted 2026 Notes, as the case may be, in the event that the market value per share of the Company’s common stock, as measured under the terms of the capped call transactions at the time of exercise, is greater than the strike price of the capped call transactions (which initially corresponds to the initial conversion price of the 2026 Notes, and is subject to certain adjustments), with such reduction and/or offset subject to a cap initially equal to approximately $14.07 (which represents a premium of approximately 70% over the last reported sale price of the Company’s common stock on November 7, 2019), subject to certain adjustments. The capped call transactions are separate transactions, entered into by the Company and are not part of the terms of the 2026 Notes.

Given that the transactions meet certain accounting criteria, the convertible note capped call transactions are recorded in stockholders’ equity, and they are not accounted for as derivatives and are not remeasured each reporting period. As of March 31, 2020, the Company had not purchased any shares under the convertible note capped call transactions.

Organization and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Our condensed consolidated financial statements include the accounts of Cytokinetics and our wholly-owned subsidiary. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. The financial statements include all adjustments (consisting only of normal recurring adjustments) that management believes are necessary for the fair statement of our financial information. These interim results are not necessarily indicative of results to be expected for the full fiscal year or any future interim period. The balance sheet as of December 31, 2019 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. The financial statements and related disclosures have been prepared with the presumption that users of the interim financial statements have read or have access to the audited financial statements for the preceding fiscal year. Accordingly, these financial statements should be read in conjunction with the audited financial statements and notes thereto contained in the Company’s Form 10-K for the year ended December 31, 2019, as filed with the Securities and Exchange Commission.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the condensed consolidated financial statements and reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, investments, accrued research and development expenses, other long-lived assets, stock-based compensation, operating lease assets and liabilities, and the valuation of deferred tax assets. We base our estimates on our historical experience and also on assumptions that we believe are reasonable; however, actual results could significantly differ from those estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-13, ‘Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. ASU 2016-13 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. ASU 2016-13 is effective for annual and interim reporting periods beginning after December 15, 2019. We adopted ASU 2016-13 as of January 1, 2020 and the adoption did not have a material impact on the Condensed Consolidated Financial Statements. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (“ASU 2018-18”), which makes targeted improvements to clarify the interaction between Topic 808, Collaborative Arrangements, and Topic 606, Revenue from Contracts with Customers. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. We adopted ASU 2018-18 on January 1, 2020 and the adoption did not have a material impact on the Condensed Consolidated Financial Statements. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04’). ASU 2020-04 provides optional guidance for a limited period of time to ease the potential burden associated with the expected market transition from the London Inter-Bank Offer Rate ("LIBOR") to alternative reference rates. Companies can apply ASU 2020-04 immediately, however the guidance will only be available until December 31, 2022. The Company’s term loan utilizes LIBOR as the reference rate and the Company is currently evaluating the impact that adopting this new accounting standard will have on our Condensed Consolidated Financial Statements and related disclosures.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Summary of Fair Value of Financial Assets Consists of Cash Equivalents and Investments Classified as Available-for-sale Securities Measured on Recurring Basis

		March 31, 2020
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	Level 1	$	46,538	$	—	$	—		$	46,538
U.S. Treasury securities	Level 1		115,391		1,047		—			116,438
Agency bonds	Level 2		28,391		83		—			28,474
Commercial paper	Level 2		6,227		5		—			6,232
Corporate obligations	Level 2		35,754		8		(103	)		35,659
		$	232,301	$	1,143	$	(103	)	$	233,341

		December 31, 2019
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	Level 1	$	31,535	$	—	$	—		$	31,535
U.S. Treasury securities	Level 1		134,845		72		(1	)		134,916
Agency bonds	Level 2		47,024		23		(9	)		47,038
Commercial paper	Level 2		10,435		4		—			10,439
Corporate obligations	Level 2		40,426		24		(7	)		40,443
		$	264,265	$	123	$	(17	)	$	264,371

Research and Development Arrangements - Additional Information (Details) - USD ($)		3 Months Ended		12 Months Ended
	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue		$ 3,825,000	$ 8,464,000
Accounts receivable		2,704,000				$ 5,163,000
Research and Development Revenues [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue		3,825,000	8,464,000
Amgen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Co-invest option payment				$ 18,800,000
Co-invest option exercised amount				$ 40,000,000
Percentage of incremental royalty receivable on annual net sales				4.00%
Amgen [Member] \| Research and Development Revenues [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue		2,300,000	4,200,000
Accounts receivable		2,300,000				3,300,000
Astellas [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition, Non-refundable upfront amendment fee					$ 35,000,000
Amount received as milestone payment					15,000,000
Revenue recognition over performance period					44,200,000
Allocated consideration					$ 94,200,000
Astellas [Member] \| Research and Development Revenues [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue		1,500,000	$ 4,300,000
Astellas OSSA Agreement [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research milestone payments		1,000,000
Accounting Standards Update 2014-09 [Member] \| Astellas [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts receivable		0				$ 1,900,000
Amgen [Member] \| Accounting Standards Update 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Pre-commercialization milestone payments eligible to receive		300,000,000
Maximum [Member] \| Astellas FSRA Agreement [Member] \| 2016 Astellas Amendment [Member] \| Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of development costs for clinical trials of reldesemtiv	$ 12,000,000
Maximum [Member] \| Astellas OSSA Agreement [Member] \| 2016 Astellas Amendment [Member] \| Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement		200,000,000
Maximum [Member] \| Amgen [Member] \| Accounting Standards Update 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Commercialization milestone payments eligible to receive		300,000,000
Minimum [Member] \| Astellas OSSA Agreement [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement		$ 250,000,000

Fair Value Measurements - Summary of Fair Value of Financial Assets Consists of Cash Equivalents and Investments Classified as Available-for-sale Securities Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - Cash and Cash Equivalents and Investments [Member] - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 232,301	$ 264,265
Unrealized Gains	1,143	123
Unrealized Losses	(103)	(17)
Fair Value	233,341	264,371
Money Market Funds [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	46,538	31,535
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	46,538	31,535
U.S. Treasury Securities [Member] \| Fair Value Measurements Using Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	115,391	134,845
Unrealized Gains	1,047	72
Unrealized Losses	0	(1)
Fair Value	116,438	134,916
Agency Bonds [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	28,391	47,024
Unrealized Gains	83	23
Unrealized Losses	0	(9)
Fair Value	28,474	47,038
Commercial Paper [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	6,227	10,435
Unrealized Gains	5	4
Unrealized Losses	0	0
Fair Value	6,232	10,439
Corporate Obligations [Member] \| Fair Value Measurements Using Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	35,754	40,426
Unrealized Gains	8	24
Unrealized Losses	(103)	(7)
Fair Value	$ 35,659	$ 40,443

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Interest Income, net	$ 723,000	$ 1,141,000
Available for sale investments, fair value	600,000	1,000,000
Available for sale investments, unrealized gain (loss)	(400,000)
Credit losses on debt securities	0	$ 0
Long-term debt, fair value	45,300,000
Convertible debt, fair value	181,500,000
Fair value of liabilities transferred from level 1 to level 2	0
Fair value of liabilities transferred from level 2 to level 1	0
Fair value of liabilities transferred into level 3	0
Fair value of liabilities transferred from level 3	$ 0

Leases - Additional Information (Detail) $ in Millions			1 Months Ended	3 Months Ended
Leases - Additional Information (Detail) $ in Millions	Jan. 01, 2021	Jan. 01, 2020	Jul. 31, 2019 USD ($) ft² USD_per_sqft	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Lease expiration year				2021
Weighted average remaining lease term				1 year 3 months 18 days
Weighted average discount rate				9.00%
Cash paid included in net cash used in operating activities				$ 2.0
Rent expense				$ 1.4	$ 1.3
Expansion Lease [Member]
Lessee Lease Description [Line Items]
Weighted average remaining lease term				3 years
Weighted average discount rate				11.50%
Area of land under lease agreement \| ft²			9,530
Initial lease term			39 months
Operating lease commencement period			2020-01
Oyster Point Lease [Member] \| California [Member]
Lessee Lease Description [Line Items]
Area of land under lease agreement \| ft²			234,892
Initial lease term			12 years
Operating lease commencement period			2021-09
Operating lease, term description			We have two consecutive five-year options to extend the lease. Subject to rent abatement for the first two months of the lease, we will be required to pay $5.45 per square foot for 159,891 square feet for the first twelve months of the lease term, which will increase at a rate of 3.5% per year. After the first twelve months of the lease, rent will be payable on the entire leased square footage.
Rent payment required to be pay for lease per square foot \| USD_per_sqft			5.45
Area of land \| ft²			159,891
Increase in operating lease rate annual payment			3.50%
Refundable lease security deposit			$ 5.1
Percentage of lease security deposit		50.00%
Lease agreement allowances for tenant improvements			$ 43.6
Undiscounted lease payments				$ 217.7
Oyster Point Lease [Member] \| California [Member] \| Forecast [Member]
Lessee Lease Description [Line Items]
Percentage of lease security deposit	50.00%

Debt - Additional Information (Detail)			3 Months Ended
Debt - Additional Information (Detail)	Nov. 13, 2019 USD ($) $ / shares shares	Nov. 07, 2019 $ / shares	Mar. 31, 2020 USD ($) Installment Day	Mar. 31, 2019 USD ($)	May 17, 2019 USD ($)
Debt Instrument [Line Items]
Interest expense			$ 4,077,000	$ 1,170,000
Purchase of capped call options associated with convertible notes			13,400,000
Cap price of capped call transactions \| $ / shares		$ 14.07
Capped call premium percentage of sale price of common stock		70.00%
Oxford and Silicon Valley Bank [Member] \| Term Loan Agreement [Member]
Debt Instrument [Line Items]
Principal amount of original loan					$ 45,000,000
Oxford and Silicon Valley Bank [Member] \| 2019 Term Loan [Member] \| Term Loan Agreement [Member]
Debt Instrument [Line Items]
Principal amount of original loan					$ 42,000,000
Interest expense			$ 1,200,000	$ 1,200,000
Stated interest rate on the amounts borrowed under the Agreement			8.05%
Prepayment fee percentage in fiscal year			3.00%
Prepayment fee percentage in year two			2.00%
Prepayment fee percentage in year three			1.00%
Oxford and Silicon Valley Bank [Member] \| 2019 Term Loan [Member] \| Amended Loan Agreement [Member]
Debt Instrument [Line Items]
Loan repayment terms			The borrowing under the Original Loan Agreement was repayable in monthly interest-only payments through November 2019 followed by 35 months of monthly payments of interest and principal
Number of instalments description			35 months of monthly payments of interest and principal
Number of instalments \| Installment			35
Debt instrument, applicable interest rate for scenario 1			8.05%
Debt instrument, base interest rate for scenario 2			6.81%
Interest rate description			Both borrowings under the Original Loan Agreement and Term Loan Agreement bear interest at an annual rate equal to the greater of (a) 8.05% or (b) the sum of 6.81% plus the 30-day U.S. LIBOR rate.
Oxford and Silicon Valley Bank [Member] \| 2019 Term Loan [Member] \| New Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Loan repayment terms			The borrowing under the Term Loan Agreement was initially repayable in monthly interest-only payments through December 31, 2020. The interest-only period was automatically extended until July 1, 2021 as a result of the Company’s initiation of a Phase 2 trial for CK-274 in cardiomyopathy and could potentially be extended through December 31, 2021 if positive results are achieved in the Phase 3 GALACTIC-HF trial for omecamtiv mecarbil in chronic heart failure, in form and content reasonably acceptable to the Lenders. The ultimate interest-only period will be followed by equal monthly payments of principal and interest to the maturity date in December 2023
Final payment fee percentage			6.00%
2026 Notes [Member]
Debt Instrument [Line Items]
Principal amount of original loan	$ 138,000,000
Number of instalments description			payable semi-annually on May 15 and December 15 of each year, beginning May 15, 2020
Convertible notes, interest rate	4.00%
Convertible notes, maturity date	Nov. 15, 2026
Convertible notes, sinking fund	$ 0
Convertible notes, shares issued \| shares	94.7811
Convertible notes, principal amount	$ 1,000
Convertible notes, initial conversion price \| $ / shares	$ 10.55
Convertible notes, type of equity security issued			common stock
Net proceeds from convertible notes, net of debt discount and issuance costs	$ 133,900,000
Convertible notes, conversion description			The 2026 Notes may be converted at the option of the holder under any of the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on March 31, 2020 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter exceeds 127.5% of the last reported sale price of the Company’s common stock on November 7, 2019; (2) during the 5 consecutive business days immediately after any 10 consecutive trading day period (such 10 consecutive trading day period, the “measurement period”) if the trading price per $1,000 principal amount of 2026 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price per share of the Company’s common stock on such trading day and the conversion rate on such trading day; (3) upon the occurrence of certain corporate events or distributions on the Company’s common stock; (4) if the Company calls the 2026 Notes for redemption; and (5) at any time from, and including, July 15, 2026 until the close of business on the scheduled trading day immediately before the maturity date, November 15, 2026. The Company will settle conversions by paying or delivering, as applicable, cash, shares of the Company’s common stock, or a combination of cash and shares of the Company’s common stock, at the Company’s election, based on the applicable conversion rate.
Convertible notes, redemption description			The 2026 Notes will be redeemable, in whole or in part, at the Company’s option at any time, and from time to time, on or after November 20, 2023 and, in the case of any partial redemption, on or before the 60th scheduled trading day before the maturity date, at a cash redemption price equal to the principal amount of the 2026 Notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date but only if the last reported sale price per share of the Company’s common stock exceeds 130% of the conversion price on (1) each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the trading day immediately before the date the Company sends the related redemption notice; and (2) the trading day immediately before the date the Company sends such notice. If a “fundamental change” (as defined in the indenture) occurs, then, subject to certain exceptions, holders may require the Company to repurchase their 2026 Notes at a cash repurchase price equal to the principal amount of the 2026 Notes to be repurchased, plus accrued and unpaid interest, if any, to, but excluding, the fundamental change repurchase date
Carrying amount of the liability component	84,200,000
Carrying amount of the equity component	$ 49,500,000
Debt instrument interest, discount rate	12.00%
Debt issuance costs	$ 5,000,000
Unamortized debt issuance cost			$ 3,000,000
Debt Instrument, Unamortized Discount			$ 49,500,000
Unamortized debt discount amortization period			6 years 8 months 12 days
If-converted value in excess of principal amount			$ 58,600,000
2026 Notes [Member] \| Equity [Member]
Debt Instrument [Line Items]
Debt issuance costs	1,900,000
2026 Notes [Member] \| Liability [Member]
Debt Instrument [Line Items]
Debt issuance costs	$ 3,100,000
Debt instrument effective interest rate			12.50%
2026 Notes [Member] \| Debt Instrument Convertible Covenant One [Member]
Debt Instrument [Line Items]
Convertible notes, percentage of conversion price			127.50%
Convertible notes, trading days \| Day			20
Convertible notes, consecutive trading days \| Day			30
2026 Notes [Member] \| Debt Instrument Convertible Covenant Two [Member]
Debt Instrument [Line Items]
Convertible notes, percentage of last reported sale price of common stock			98.00%
Convertible notes, trading days \| Day			5
Convertible notes, consecutive trading days \| Day			10

Debt - Schedule of Future Minimum Payments under Term Loan Agreement (Detail) - Term Loan Agreement [Member] - Oxford and Silicon Valley Bank [Member] $ in Thousands	Mar. 31, 2020 USD ($)
Debt Instrument [Line Items]
2020 remainder	$ 2,785
2021	12,519
2022	20,264
2023	23,381
Future minimum payments	58,949
Long-term debt, alternative
Future minimum payments	58,949
Less: Interest and final payment	(13,949)
Term Loan, gross	$ 45,000

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Common stock, par value	$ 0.001	$ 0.001

Net Loss Per Share - Instruments Excluded from Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	27,148	6,952
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	9,092	5,844
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	187	142
Restricted Stock and Performance Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	1,134	881
Shares Issuable Related to the ESSP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	60	85
Shares Issuable Upon Conversion of Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	16,675	0

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued liabilities:
Clinical and preclinical costs	$ 2,446	$ 2,215
Compensation related	5,229	8,343
Other accrued expenses	2,002	1,565
Total accrued liabilities	$ 9,677	$ 12,123

Leases - Schedule of Undiscounted Future Non-cancellable Lease Payments under the Lease Agreements (Detail) $ in Thousands	Mar. 31, 2020 USD ($)
Leases [Abstract]
2020 remainder	$ 3,951
2021	4,616
2022	12,694
2023	16,195
2024	16,648
Thereafter	170,919
Total undiscounted future lease payments	225,023
Less: Undiscounted lease payments related to Oyster Point Lease	(217,667)
Less: Present value adjustments	(552)
Total lease liability	$ 6,804

Liability Related to Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2017	Mar. 31, 2020	Mar. 31, 2019
Liability Related to Sale of Future Royalties [Line Items]
Non-cash interest expense recognized		$ 5,706	$ 4,819
Royalty Purchase Agreement [Member]
Liability Related to Sale of Future Royalties [Line Items]
Cash payment under Royalty Agreement	$ 90,000
Non-cash interest expense recognized		$ 5,700	$ 4,800

Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Accumulated deficit incurred	$ (904,421)	$ (865,016)
Cash requirements term	12 months

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Claims settlement under Section 16(b)	$ 2,151	$ 0
Oxford and Silicon Valley Bank [Member] \| Loan and Security Agreement [Member] \| 2019 Term Loan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding to purchase upon exercise of common stock	21,595
Warrants exercise price	$ 10.42
Outstanding warrants	187,019
Outstanding warrants, weighted average exercise price	$ 7.62
Warrants expiration date	2030-01
Amortization of debt discount	$ 200