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Balance Sheet Components - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 28,725	$ 27,065
Less: Accumulated depreciation and amortization	(24,195)	(23,861)
Total property and equipment, net	4,530	3,204
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	18,741	17,916
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,940	2,882
Office Equipment, Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,823	1,137
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 5,221	$ 5,130

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 36,433	$ 42,256
Short-term investments	188,679	156,475
Accounts receivable	5,163	2,231
Contract assets	0	4,554
Prepaid expenses and other current assets	3,477	2,158
Total current assets	233,752	207,674
Long-term investments	42,650	0
Property and equipment, net	4,530	3,204
Operating lease right-of-use assets and other assets	8,882	300
Total assets	289,814	211,178
Current liabilities:
Accounts payable	8,160	3,764
Accrued liabilities	12,123	15,757
Current portion of long-term debt	0	2,607
Short-term lease liability	4,616	0
Other current liabilities	1,124	66
Total current liabilities	26,023	22,194
Term loan, net	45,052	39,806
Convertible notes, net	84,205	0
Liability related to the sale of future royalties, net	143,276	122,473
Long-term lease liability	2,195	771
Total liabilities	300,751	185,244
Commitments and contingencies	0	0
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value: Authorized: 10,000,000 shares; Issued and outstanding: none	0	0
Common stock, $0.001 par value: Authorized: 163,000,000 shares Issued and outstanding: 59,172,124 shares at December 31, 2019 and 54,717,906 shares at December 31, 2018	59	55
Additional paid-in capital	853,341	768,703
Accumulated other comprehensive income	679	500
Accumulated deficit	(865,016)	(743,324)
Total stockholders’ equity (deficit)	(10,937)	25,934
Total liabilities and stockholders’ equity (deficit)	$ 289,814	$ 211,178

Consolidated Statements of Stockholders' Equity (Deficit) - 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, 2017	$ 109,842	$ 54	$ 755,526	$ 343	$ (646,081)
Beginning Balance, shares at Dec. 31, 2017		53,960,832
Exercise of stock options, value	3,173	$ 1	3,172	0	0
Exercise of stock options, shares		422,819
Issuance under Employee Stock Purchase Plan, value	928	$ 0	928	0	0
Issuance under Employee Stock Purchase Plan, shares		144,822
Vesting of restricted stock units, net of taxes withheld, value	(866)	$ 0	(866)	0	0
Vesting of restricted stock units, net of taxes withheld, shares		189,433
Issuance of warrants	182	$ 0	182	0	0
Stock-based compensation	9,761	0	9,761	0	0
ASC 606 Adoption \| ASC 606 [Member]	9,046	0	0	0	9,046
Other comprehensive loss	157	0	0	157	0
Net loss	(106,289)	0	0	0	(106,289)
Ending Balance at Dec. 31, 2018	25,934	$ 55	768,703	500	(743,324)
Ending Balance, shares at Dec. 31, 2018		54,717,906
Exercise of stock options, value	1,017	$ 0	1,017	0	0
Exercise of stock options, shares		131,909
Issuance of common stock under at-the-market offering, net of issuance costs	36,214	$ 4	36,210	0	0
Issuance of common stock under at-the-market offering, net of issuance costs, shares		3,984,849
Issuance under Employee Stock Purchase Plan, value	1,108	$ 0	1,108	0	0
Issuance under Employee Stock Purchase Plan, shares		172,113
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
Issuance of warrants	185	$ 0	185	0	0
Equity component of convertible notes	49,477	0	49,477	0	0
Capped call options associated with convertible notes	(13,386)	0	(13,386)	0	0
Stock-based compensation	10,759	0	10,759	0	0
Other comprehensive loss	179	0	0	179	0
Net loss	(121,692)	0	0	0	(121,692)
Ending Balance at Dec. 31, 2019	$ (10,937)	$ 59	$ 853,341	$ 679	$ (865,016)
Ending Balance, shares at Dec. 31, 2019		59,172,124

Income Taxes - Summary of Deferred Tax Assets, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 143,228	$ 121,748
Tax credits	67,892	64,797
Liability related to sale of future royalties	35,213	26,294
Reserves and accruals	8,690	5,772
Capitalized R&D	3,949	4,614
Long-term lease liability	1,674	0
Depreciation and amortization	722	586
Other	58	0
Total noncurrent deferred tax assets	261,426	223,811
Deferred tax liabilities:
Accounting method change	(2,047)	(2,682)
Operating lease right-of-use assets	(1,484)	0
Convertible notes	(12,011)	0
Other	0	(20)
Total noncurrent deferred tax liabilities	(15,542)	(2,702)
Less: Valuation allowance	(245,884)	(221,109)
Net deferred tax assets	$ 0	$ 0

Stockholders' Equity

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Stockholders' Equity

Note 9 — Stockholders’ Equity

Equity Incentive Plan

Our amended and restated 2004 Equity Incentive Plan (the “2004 Plan”) provides for us to grant incentive stock options, nonstatutory stock options, restricted stock, stock appreciation rights, restricted stock units, performance shares and performance units to employees, directors and consultants. We may grant options for terms of up to ten years at prices not lower than 100% of the fair market value of our common stock on 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. As of December 31, 2019, we have 4.4 million shares of common stock reserved and available for issuance under the 2004 Plan.

Stock option activity in 2019 was as follows:

	Stock Options Outstanding			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in millions)
Balance at December 31, 2018		6,454,037		$	8.72
Granted		1,785,673			8.41
Exercised		(126,793	)		7.78
Forfeited		(353,905	)		10.44
Balance at December 31, 2019		7,759,012		$	8.59		6.5	$	18.8
Exercisable at December 31, 2019		5,349,164		$	8.57		5.6	$	13.2

We expect all outstanding options to vest. The intrinsic value of stock options exercised, calculated based on the difference between the market value at the date of exercise and the exercise price, was $0.5 million for 2019 and $0.7 million for 2018. The intrinsic value of stock options outstanding at December 31, 2019 was $18.8 million.

Restricted stock unit activity in 2019 was as follows:

	Number of Restricted Stock Units			Weighted Average Award Date Fair Value per Share
Balance at December 31, 2018		546,500		$	8.53
Granted		607,150			7.14
Released		(266,500	)		8.84
Forfeited		(48,075	)		7.34
Balance at December 31, 2019		839,075		$	7.49

RSUs generally vest annually over two to three years. For 2019, the fair value of RSUs vested, calculated based on the units vested multiplied by the closing price of our common stock on the date of vesting, was $1.9 million.

Employee Stock Purchase Plan

Under our 2015 Employee Stock Purchase Plan (the “ESPP”), employees may purchase common stock up to a specified maximum amount at a price equal to 85% of the fair market value at certain plan-defined dates.

We issued 172,113 shares at an average price of $6.43 per share during 2019 and 144,822 shares at an average price of $6.40 per share in 2018 pursuant to the ESPP. At December 31, 2019, we have 81,504 shares of common stock reserved for issuance under the ESPP.

Stock-Based Compensation Expense

We use 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 fair value of share-based payments was estimated on the date of grant based on the following assumptions:

Year Ended December 31, 2019

Year Ended December 31, 2018

Options

ESPP

Options

ESPP

Risk-free interest rate

1.6% to 3.0%

1.8% to 2.4%

2.3% to 3.0%

1.5% to 2.5%

Volatility

73% to 76%

73% to 74%

Expected term in years

6.5

0.6

6.5

0.5

Expected dividend yield

We use U.S. Treasury zero-coupon issues with remaining terms similar to the expected terms of the options for the risk-free interest rate. We use our own volatility history based on its stock’s trading history and our own historical exercise and forfeiture activity to estimate expected term for option grants. We do not anticipate paying dividends in the foreseeable future and use an expected dividend yield of zero. We do not estimate forfeitures in our stock-based compensation.

We measure compensation expense for restricted stock units at fair value on the date of grant and recognize the expense over the expected vesting period. We recognize stock-based compensation expense on a ratable basis over the requisite service period, generally the vesting period of the award for share-based awards.

Stock-based compensation expense for 2019 and 2018 was as follows (in thousands):

	Years Ended December 31,
	2019		2018
Research and development	$	4,260	$	5,101
General and administrative		6,499		4,660
	$	10,759	$	9,761

Non-cash stock-based compensation expense for share-based awards to non-employees was $0.2 million in 2019 and $0.1 million in 2018.

As of December 31, 2019, we expect to recognize $13.5 million of unrecognized compensation cost related to unvested stock options over a weighted-average period of 2.5 years and $3.5 million of unrecognized compensation cost related to unvested restricted stock over a weighted-average period of 1.7 years.

Warrants

Pursuant to the Term Loan agreement described in Note 7 - Debt, we issued a warrant with an exercise price of $9.76 per share to purchase 23,065 shares of our common stock in 2019. The warrant was fully exercisable and expires in May 2029. As of December 31, 2019, warrants to purchase 165,424 shares of our common stock with a weighted average exercise price of $7.25 per share were outstanding. All outstanding warrants are fully exercisable and expire ten years after issuance.

We determined the fair value of the warrants issued in 2019 to be $0.2 million and recorded this fair value as additional debt discount that is being amortized to interest expense over the term of the related debt.

Committed Equity Offering

In 2019, we terminated the original Controlled Equity Offering^SM Sales Agreement (the “ATM Facility”) with Cantor Fitzgerald & Co. (“Cantor”) for the sale, in our sole discretion, of shares of our common stock, having an aggregate offering price of up to $75.0 million through Cantor and we entered into a new sales agreement (the “New ATM Facility”) with Cantor, which provides for the sale, in our sole discretion, of shares of our common stock having an aggregate offering price of up to $85.0 million through Cantor, as our sales agent. The issuance and sale of these shares by us pursuant to the New ATM Facility are deemed “at the market” offerings and are registered under the Securities Act of 1933, as amended. We pay a commission of up to 3.0% of gross sales proceeds of any common stock sold under the New ATM Facility. In 2019, we issued 3,984,849 shares of common stock for net proceeds of $36.2 million under the New ATM Facility. The New ATM Facility expires in January 2020.

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of stock options outstanding	$ 18,800
Non-cash stock-based compensation expense	$ 10,759	$ 9,761
Warrants outstanding to purchase upon exercise of common stock	23,065
Warrants exercise price	$ 9.76
Warrants expiration date	2029-05
Outstanding warrants	165,424
Outstanding warrants, weighted average exercise price	$ 7.25
Expiry period of warrants after date of issuance	10 years
Amortization of discount on debt	$ 200
Commision of gross sales proceeds	3.00%
Net proceeds of issuance of common stock	$ 36,214	0
New ATM Facility [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock under at-the-market offering, net of issuance costs, shares	3,984,849
Net proceeds of issuance of common stock	$ 36,200
Agreement expiration date	Jan. 31, 2020
Maximum [Member] \| ATM Facility [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock offering price	$ 75,000
Maximum [Member] \| New ATM Facility [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock offering price	85,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vested restricted stock units, total fair value	1,900
Unrecognized compensation cost	$ 3,500
Weighted-average period	1 year 8 months 12 days
Restricted Stock Units (RSUs) \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	2 years
Restricted Stock Units (RSUs) \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 13,500
Weighted-average period	2 years 6 months
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%
Shares of common stock reserved for issuance	4,400,000
Shares of common stock available for issuance	4,400,000
Share based compensation, options exercised, total intrinsic value	$ 500	$ 700
Intrinsic value of stock options outstanding	$ 18,800
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	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	4 years
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	81,504
Issuance of common stock pursuant to ESPP, shares	172,113	144,822
Issuance of common stock pursuant to ESPP, per share	$ 6.43	$ 6.40
Non-employee Stock-Based Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 200	$ 100

Debt

12 Months Ended

Dec. 31, 2019

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.

On May 17, 2019 (the “Closing Date”), we entered into a new loan and security agreement (the “Term Loan Agreement”) with the Lenders for $45.0 million (the “Term Loan”), and terminated the Original Loan Agreement. The proceeds of the Term Loan were used in part to repay in full all of the outstanding term loans under the Original Loan Agreement in an aggregate principal amount of $42.0 million. On November 6, 2019 and November 7, 2019, the Company entered into a First Amendment and a Second Amendment to the Term Loan Agreement. The Term Loan Agreement, as amended, permits the issuance of the Convertible Notes and Capped Call Transactions discussed below.

The Term Loan was accounted for as a debt modification in a non-troubled debt restructuring 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 lender 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 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 is repayable in monthly interest-only payments through December 31, 2020. The interest only period may be extended for six or twelve months if both of the following milestones occur: (i) specified events related to the development of (a) reldesemtiv, a novel fast skeletal muscle troponin activator, in spinal muscular atrophy or amyotrophic lateral sclerosis, or (b) CK-3773274, a novel cardiac myosin inhibitor, in cardiomyopathy; and/or (ii) specified results from GALACTIC-HF, a Phase 3 trial of omecamtiv mecarbil, a novel cardiac myosin activator. 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 was $5.2 million and $3.8 million for 2019 and 2018, respectively. As of December 31, 2019, the interest rate applicable to borrowings under the Term Loan was 8.57%.

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 December 31, 2019, 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	$	3,921
2021		18,312
2022		17,009
2023		20,291
Future minimum payments		59,533
Less: Interest and final payment		(14,533	)
Term Loan, gross	$	45,000

Convertible Notes

On November 13, 2019, the Company issued $138.0 million aggregate principal amount of 4.0% convertible senior notes due 2026 (the “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 130% of the conversion price on each applicable trading day; (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 December 31, 2019, the unamortized debt issuance cost for the 2026 Notes was $3.1 million on the consolidated balance sheet.

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

	Year ended December 31, 2019
Contractual interest expense	$	721
Amortization of debt discount		673
Amortization of debt issuance costs		6
Total interest costs recognized	$	1,400

The effective interest rate on the liability component of the Notes due 2026 was 12.5% for the year ended December 31, 2019, which remains unchanged from the date of issuance. The remaining unamortized debt discount was $50.7 million as of December 31, 2019, and will be amortized over approximately 7.0 years.

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 December 31, 2019, the Company had not purchased any shares under the convertible note capped call transactions.

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

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

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):

	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

	December 31, 2018
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	Level 1	$	34,771	$	—	$	—		$	34,771
U.S. Treasury securities	Level 1		56,999		—		(41	)		56,958
Agency bonds	Level 2		61,792		1		(14	)		61,779
Commercial paper	Level 2		19,448		—		(13	)		19,435
Corporate obligations	Level 2		17,644		2		(8	)		17,638
		$	190,654	$	3	$	(76	)	$	190,581

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 02, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	CYTK
Entity Registrant Name	CYTOKINETICS INC
Entity Central Index Key	0001061983
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 Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		59,450,437
Entity Public Float			$ 653.1
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
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
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Portions of the Registrant’s Proxy Statement for its 2020 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission, no later than 120 days after the end of the fiscal year, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Research and Development Arrangements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	$ 26,868,000	$ 31,501,000
Accounts receivable	5,163,000	2,231,000
Contract assets	0	4,554,000
2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets	0	4,600,000
Research and Development Revenues [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	26,868,000	26,368,000
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	13,800,000	$ 1,900,000
Amgen [Member] \| Research and Development Revenues [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts receivable	3,300,000	1,900,000
Astellas [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	13,106,000	29,386,000
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
Accounting Standards Update 2014-09 [Member] \| Astellas [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts receivable	1,900,000	$ 300,000
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] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research milestone payments	2,000,000
Maximum [Member] \| 2016 Astellas Amendment [Member] \| Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement	200,000,000
Maximum [Member] \| Astellas [Member] \| 2016 Astellas Amendment [Member] \| Non Neuromuscular Indications
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement	95,000,000
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 [Member] \| 2016 Astellas Amendment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement	600,000,000
Minimum [Member] \| Astellas [Member] \| 2016 Astellas Amendment [Member] \| SMA and Other Neuromuscular Indications [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential amount receivable under collaboration agreement	$ 100,000,000

Organization and Accounting Policies

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Accounting Policies

Note 1 — Organization and Accounting Policies

Organization

Cytokinetics, Incorporated (the “Company”, “we” or “our”) was incorporated under the laws of the state of Delaware on August 5, 1997. We are 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 $865.0 million since inception and there can be no assurance that we will attain profitability. We had a net loss of $121.7 million and net cash used in operations of $90.9 million for the year ended December 31, 2019. Cash, cash equivalents and investments increased to $267.8 million at December 31, 2019 from $198.7 million at December 31, 2018. We anticipate that we 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, government grants and interest income. Until we achieve profitable operations, we intend to continue to fund operations through payments from strategic collaborations, additional sales of equity securities, grants and debt financings. We have never generated revenues from commercial sales of our drugs and may not have drugs to market for at least several years, if ever. Our success is dependent on our ability to enter into new strategic collaborations and/or raise additional capital and to successfully develop and market one or more of our drug candidates. As a result, we may choose to raise additional capital through equity or debt financings to continue to fund operations in the future. We cannot be certain that sufficient funds will be available from such a financing or through a collaborator when required or on satisfactory terms. Additionally, there can be no assurance that our drug candidates will be accepted in the marketplace or that any future products can be developed or manufactured at an acceptable cost. These factors could have a material adverse effect on our future financial results, financial position and cash flows.

Based on the current status of our research and development plans, we believe that our existing cash, cash equivalents and investments will be sufficient to fund our cash requirements for at least the next 12 months after the issuance of the consolidated financial statements. If, at any time, our prospects for financing our research and development programs decline, we may decide to reduce research and development expenses by delaying, discontinuing or reducing our 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. 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 Incorporated 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. Certain prior period amounts have been reclassified to conform the prior period presentation to the current year.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject us to concentrations of risk consist principally of cash and cash equivalents, investments, and accounts receivable.

Our cash, cash equivalents and investments are invested in deposits with two major financial institutions in the United States. Deposits in these banks may exceed the amount of insurance provided on such deposits.

Our exposure to credit risk associated with non-payment is limited to our strategic partners Amgen Inc. (“Amgen”) and Astellas Pharma Inc. (“Astellas”) and any material non-payment from our partners would result in a material breach of the agreements underlying our strategic partnerships.

Drug candidates we develop may require approvals or clearances from the U.S. Food and Drug Administration (“FDA”) or other regulatory agencies prior to commercial sales. There can be no assurance that our drug candidates will receive any of the required approvals or clearances. If we were to be denied approval, or clearance or any such approval or clearance was to be delayed, it would have a material adverse impact on us.

Cash and Cash Equivalents

We consider 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 investments. Our investments consist of U.S. Treasury securities, agency bonds, commercial paper, corporate debt and money market funds. We designate all investments as available-for-sale and report them at fair value, based on quoted market prices, with unrealized gains and losses recorded in accumulated other comprehensive loss. The cost of securities sold is based on the specific-identification method. Investments with original maturities greater than three months and remaining maturities of one year or less are classified as short-term investments. Investments with remaining maturities greater than one year are classified as long-term investments. The amortized cost of debt securities in this category is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization is included in Interest and other income, net. Recognized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in Interest and other income, net. Interest and dividends on securities classified as available-for-sale are included in Interest and other income, net.

Other-than-temporary impairment. All of our available-for-sale investments are subject to a periodic impairment review. We recognize an impairment charge when a decline in the fair value of investments below the cost basis is judged to be other-than-temporary. Factors we consider in assessing whether an other-than-temporary impairment has occurred include: the nature of the investment; whether the decline in fair value is attributable to specific adverse conditions affecting the investment; the financial condition of the investee; the severity and the duration of the impairment; and whether we have the intent and ability to hold the investment to maturity. When we determine that an other-than-temporary impairment has occurred, the investment is written down to its market value at the end of the period in which it is determined that an other-than-temporary decline has occurred.

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.

Impairment of Long-lived Assets

We review 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. Impairment is measured as the amount by which the carrying amount of a long-lived asset exceeds its fair value. We would recognize an impairment loss when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are materially less than its carrying amount.

Leases

We adopted Accounting Standards Update No. 2016-02, Leases (“Topic 842”) on January 1, 2019 using the modified retrospective approach. In adopting Topic 842, we recognized a right-of-use asset and a short-term and long-term lease liability on our consolidated balance sheets for our existing facilities lease that expires in 2021 (the “Lease”). The right-of-use asset is based on the liability adjusted for any prepaid or deferred rent. We determined the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. In determining the present value of lease payments, we estimated our incremental borrowing rate based on information available when we adopted Topic 842. We base the lease liability on the present value of remaining lease payments over the remaining term of the Lease, using an estimated rate of interest that we would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. We evaluated our other contracts and determined that, except for the Lease, none of our contracts contained a lease as defined in Topic 842.

We elected the package of practical expedients permitted under the transition guidance within Topic 842, which among other things, allowed us to carry forward the historical lease classification of those leases in place as of January 1, 2019. We also elected to exclude from our consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for our long-term facilities lease.

The impact on the consolidated balance sheets as of January 1, 2019 was as follows (in thousands):

Balance sheet account description	ASC 840 January 1, 2019			ASC 842 January 1, 2019			Impact of adoption
Deferred rent classified as accrued liabilities	$	(323	)	$	—		$	323
Deferred rent classified as other long-term liabilities		(773	)		—			773
Short-term lease liability		—			(4,460	)		(4,460	)
Long-term lease liability		—			(6,227	)		(6,227	)
Operating lease right-of-use assets and other assets		—			9,591			9,591

We recognize rent expense for operating leases on a straight-line basis over the lease term in operating expenses on the consolidated statements of operations.

Prior period amounts continue to be reported in accordance with our historic accounting under previous lease guidance, ASC 840, Leases (“Topic 840”).

Revenue Recognition

On January 1, 2018, we adopted Topic 606, Revenue from Contracts with Customers (“Topic 606”), using the modified retrospective method. On January 1, 2018, we recognized a contract asset of $16.7 million and increased our contract liability by $7.7 million and reduced our accumulated deficit by $9.0 million for the effect of adopting Topic 606.

We recognize revenue when we transfer promised goods or services to customers in an amount that reflects the consideration for those goods or services. To recognize revenue from a contract with a customer, we:

(i) identify our contracts with our customers;

(ii) identify our distinct performance obligations in each contract;

(iii) determine the transaction price of each contract;

(iv) allocate the transaction price to the performance obligations; and

(v) recognize revenue as we satisfy our performance obligations.

At contract inception, we assess the goods or services promised within each contract and assess whether each promised good or service is distinct and determine those that are performance obligations. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

Collaborative Arrangements

We enter into collaborative arrangements with partners that typically include payment to us for one of more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; and (iv) research and development cost reimbursements. Each of these payments results in collaboration or other revenues. Where a portion of non-refundable up-front fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied.

As part of the accounting for these arrangements, we must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligations. The stand-alone selling price may include such items as, forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, to determine the transaction price to allocate to each performance obligation.

For our collaboration agreements that include more than one performance obligation, such as a license combined with a commitment to perform research and development services, we make judgments to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. We evaluate our progress each reporting period and, if necessary, adjust the measure of a performance obligation and related revenue recognition.

License Fees: If a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front license fees. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition.

Milestone Payments: We use judgment to determine whether a milestone is considered probable of being reached. Using the most likely amount method, we include the value of a milestone payment in the consideration for a contract at inception if we then conclude achieving the milestone is more likely than not. Otherwise, we exclude the value of a milestone payment from contract consideration at inception and recognize revenue for a milestone at a later date, when we judge that it is probable the milestone will be achieved. If we conclude it is probable that a significant revenue reversal would not occur, the associated milestone is included in the transaction price. We then allocate the transaction price to each performance obligation on a relative stand-alone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, we re-evaluate the probability of achievement of such milestones and any related constraint, and if necessary, adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration and other revenues and earnings in the period of adjustment.

Royalties: For contracts that include sales-based royalties, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied. To date, we have not recognized any royalty revenues resulting from contracts.

Research and Development Cost Reimbursements: Our Astellas and Amgen arrangements include promises of research and development services. We have determined that these services collectively are distinct from the licenses provided to Astellas and Amgen and as such, these promises are accounted for as a separate performance obligation recorded over time. We recognize revenue for these services as the performance obligations are satisfied, which we estimate using internal development costs incurred.

Accrued Research and Development Expenditures

A substantial portion of our preclinical studies and all of our clinical trials have been performed by third-party contract research organizations (“CROs”) and other vendors and our accruals for expenses for preclinical studies and clinical trials may be significant. 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, milestones achieved and percentage of work completed to date. We monitor patient enrollment levels and related activities to the extent practicable through internal reviews, correspondence and status meetings with CROs, and review of contractual terms. We depend on the timeliness and accuracy of data provided by our CROs and other vendors to accrue expenses. If we receive and rely on incomplete or inaccurate data, accruals and expenses may be too high or too low at a given point in time and corresponding adjustments to accruals and expenses would be made in future periods when the actual expense becomes known.

Liability Related to Sale of Future Royalties

We treat the Liability related to sale of future royalties as a debt financing, to be amortized under the effective interest rate method over the life of the related royalty stream.

The Liability related to sale of future royalties and the debt amortization are based on our current estimates of future royalties expected to be paid over the life of the arrangement. We will periodically assess the expected royalty payments using a combination of internal projections and forecasts from external sources. To the extent our future estimates of future royalty payments are greater or less than previous estimates or the estimated timing of such payments is materially different than previous estimates, we will adjust the Liability related to sale of future royalties and prospectively recognize the related non-cash interest expense.

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

We account for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized.

We recognize uncertain tax positions taken or expected to be taken on a tax return. Tax positions are initially recognized when it is more likely than not that the position will be sustained upon examination by the tax authorities. Such tax positions are initially and subsequently measured as the largest amount of tax benefit that is more likely than not of being realized upon ultimate settlement with the tax authority assuming full knowledge of the position and relevant facts.

We recognize interest accrued related to unrecognized tax benefits and penalties as income tax expense.

In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (“ASU 2019-12”), as part of its Simplification Initiative to reduce the cost and complexity in accounting for income taxes. ASU 2019-12 removes certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. ASU 2019-12 also amends other aspects of Topic 740, Income Taxes, to help simplify and promote consistent application of GAAP. The guidance is effective for interim and annual periods beginning after December 15, 2020, with early adoption permitted. We early adopted ASU 2019-12 in 2019 and it did not have a material impact on the Consolidated Financial Statements.

The only aspect of ASU 2019-12 that had a material impact on our consolidated financial statements was the removal of the exception related to intraperiod tax allocation. Starting in 2019, we followed the general intraperiod allocation of tax expense. We have a loss from continuing operations and subsequent to the adoption of ASU 2019-12, we determined the amount attributable to continuing operations without regard to the tax effect of other items. The ASU 2019-12 amendment related to intraperiod tax allocation was applied prospectively.

Had the Company not adopted ASU 2019-12, a $12 million deferred tax benefit would have been recognized along with corresponding decreases to net loss and accumulated deficit. The Company had no intraperiod tax allocation items in prior years.

Due to our net loss position, the income tax benefit generated without the adoption of ASU 2019-12 was a non-cash benefit. The adoption of ASU 2019-12 did not impact our cash flows.

Stock-Based Compensation

We maintain equity incentive plans under which incentive stock options may be granted to employees and nonqualified stock options, restricted stock awards, restricted stock units and stock appreciation rights may be granted to employees, directors, consultants and advisors. In addition, we maintain an employee stock purchase plan (“ESPP”) under which employees may purchase shares of our common stock through payroll deductions.

Stock-based compensation expense related to stock options granted to employees and directors is recognized based on the grant date estimated fair values using the Black Scholes option pricing model. The value of the portion of the award that is ultimately expected to vest is recognized as expense ratably over the requisite service period.

Stock-based compensation expense related to restricted stock units granted to employees is recognized based on the grant-date fair value of each award and recorded as expense over the vesting period using the ratable method.

Stock-based compensation expense related to the ESPP is recognized based on the fair value of each award estimated on the first day of the offering period using the Black Scholes option pricing model and recorded as expense over the service period using the straight-line method.

Amortization of Debt Discount and Issuance Costs

Debt discount and issuance costs, consisting of legal and other fees directly related to the debt as well as the discount created by the bifurcation of the equity component and the debt component of the 2026 Notes, are offset against gross proceeds from the issuance of debt and are amortized to interest expense over the estimated life of the debt based on the effective interest method.

Recent Accounting Standards

In November 2018, the Financial Accounting Standards Board (“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 plan to adopt ASU 2018-18 on January 1, 2020 and do not expect the adoption to have a material impact on the Consolidated Financial Statements.

In June 2016, the 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 plan to adopt ASU 2016-13 on January 1, 2020 and do not expect the adoption to have a material impact on the Consolidated Financial Statements.

Leases - Additional Information (Detail) $ in Thousands			1 Months Ended	12 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Jan. 01, 2021	Jan. 01, 2020	Jul. 31, 2019 USD ($) ft² USD_per_sqft	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Lessee Lease Description [Line Items]
Cash paid included in net cash used in operating activities				$ 5,000
Lease expiration year				2021
Weighted average remaining lease term				1 year 6 months
Weighted average discount rate				9.00%
Undiscounted lease payments				$ 1,335
Future minimum lease payments under noncancelable operating leases in 2019					$ 4,700
Future minimum lease payments under noncancelable operating leases in 2020					4,800
Future minimum lease payments under noncancelable operating leases in 2021					2,500
Rent expense				5,100	$ 5,000
Expansion Lease [Member]
Lessee Lease Description [Line Items]
Area of land under lease agreement \| ft²			9,530
Initial lease term			39 months
Operating lease commencement period			2020-01
Undiscounted lease payments				1,300
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
Undiscounted lease payments				$ 217,700
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			$ 5,100
Lease agreement allowances for tenant improvements			$ 34,100
Oyster Point Lease [Member] \| California [Member] \| Forecast [Member]
Lessee Lease Description [Line Items]
Percentage of lease security deposit	50.00%	50.00%

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Summary of Stock Option Activity

Stock option activity in 2019 was as follows:

	Stock Options Outstanding			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in millions)
Balance at December 31, 2018		6,454,037		$	8.72
Granted		1,785,673			8.41
Exercised		(126,793	)		7.78
Forfeited		(353,905	)		10.44
Balance at December 31, 2019		7,759,012		$	8.59		6.5	$	18.8
Exercisable at December 31, 2019		5,349,164		$	8.57		5.6	$	13.2

Summary of Restricted Stock Unit Activity

Restricted stock unit activity in 2019 was as follows:

	Number of Restricted Stock Units			Weighted Average Award Date Fair Value per Share
Balance at December 31, 2018		546,500		$	8.53
Granted		607,150			7.14
Released		(266,500	)		8.84
Forfeited		(48,075	)		7.34
Balance at December 31, 2019		839,075		$	7.49

Fair Value of Share-Based Payments was Estimated on Date of Grant Based on Assumptions

Year Ended December 31, 2019

Year Ended December 31, 2018

Options

ESPP

Options

ESPP

Risk-free interest rate

1.6% to 3.0%

1.8% to 2.4%

2.3% to 3.0%

1.5% to 2.5%

Volatility

73% to 76%

73% to 74%

Expected term in years

6.5

0.6

6.5

0.5

Expected dividend yield

Summary of Stock-Based Compensation Expense

Stock-based compensation expense for 2019 and 2018 was as follows (in thousands):

	Years Ended December 31,
	2019		2018
Research and development	$	4,260	$	5,101
General and administrative		6,499		4,660
	$	10,759	$	9,761

Organization and Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization

Use of Estimates

Basis of Presentation

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject us to concentrations of risk consist principally of cash and cash equivalents, investments, and accounts receivable.

Cash and Cash Equivalents

We consider all highly liquid investments with a maturity of three months or less at the time of purchase to be cash equivalents.

Investments

Property and Equipment, net

Impairment of Long-lived Assets

Leases

The impact on the consolidated balance sheets as of January 1, 2019 was as follows (in thousands):

Balance sheet account description	ASC 840 January 1, 2019			ASC 842 January 1, 2019			Impact of adoption
Deferred rent classified as accrued liabilities	$	(323	)	$	—		$	323
Deferred rent classified as other long-term liabilities		(773	)		—			773
Short-term lease liability		—			(4,460	)		(4,460	)
Long-term lease liability		—			(6,227	)		(6,227	)
Operating lease right-of-use assets and other assets		—			9,591			9,591

We recognize rent expense for operating leases on a straight-line basis over the lease term in operating expenses on the consolidated statements of operations.

Prior period amounts continue to be reported in accordance with our historic accounting under previous lease guidance, ASC 840, Leases (“Topic 840”).

Revenue Recognition

(i) identify our contracts with our customers;

(ii) identify our distinct performance obligations in each contract;

(iii) determine the transaction price of each contract;

(iv) allocate the transaction price to the performance obligations; and

(v) recognize revenue as we satisfy our performance obligations.

Collaborative Arrangements

Accrued Research and Development Expenditures

Liability Related to Sale of Future Royalties

We treat the Liability related to sale of future royalties as a debt financing, to be amortized under the effective interest rate method over the life of the related royalty stream.

Research and Development Expenditures

Income Taxes

We recognize interest accrued related to unrecognized tax benefits and penalties as income tax expense.

Due to our net loss position, the income tax benefit generated without the adoption of ASU 2019-12 was a non-cash benefit. The adoption of ASU 2019-12 did not impact our cash flows.

Stock-Based Compensation

Amortization of Debt Discount and Issuance Costs

Recent Accounting Pronouncements

Recent Accounting Standards

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Reconciliation of Statutory Federal Income Tax Rate to Effective Tax Rate

The following reconciles the statutory federal income tax rate to our effective tax rate:

	Years Ended December 31,
	2019			2018
Tax at federal statutory tax rate		21	%		21	%
State tax, net of federal benefits		3	%		0	%
Change in state effected rates		4	%		(4	)%
Tax credits, net		3	%		1	%
Change in valuation allowance		(30	)%		(17	)%
Stock-based compensation		(1	)%		(1	)%
Total		(0	)%		(0	)%

Summary of Deferred Tax Assets, Net

Deferred tax assets, net, reflecting 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, were as follows (in thousands):

	As of December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	143,228		$	121,748
Tax credits		67,892			64,797
Liability related to sale of future royalties		35,213			26,294
Reserves and accruals		8,690			5,772
Capitalized R&D		3,949			4,614
Long-term lease liability		1,674			—
Depreciation and amortization		722			586
Other		58			—
Total noncurrent deferred tax assets		261,426			223,811
Deferred tax liabilities:
Accounting method change		(2,047	)		(2,682	)
Operating lease right-of-use assets		(1,484	)		—
Convertible notes		(12,011	)		—
Other		—			(20	)
Total noncurrent deferred tax liabilities		(15,542	)		(2,702	)
Less: Valuation allowance		(245,884	)		(221,109	)
Net deferred tax assets	$	—		$	—

Schedule of Activity Related to our Gross Unrecognized Tax Benefits

Activity related to our gross unrecognized tax benefits were (in thousands):

	Years Ended December 31,
	2019		2018
Balance at the beginning of the year	$	9,475	$	9,365
Decrease related to prior year tax positions		—		—
Increase related to current year tax positions		447		110
Balance at the end of the year	$	9,922	$	9,475

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Note 10 — Income Taxes

We did not record an income tax provision in 2019 and 2018 because we had net taxable losses. Our significant jurisdictions are the United States and California.

The following reconciles the statutory federal income tax rate to our effective tax rate:

	Years Ended December 31,
	2019			2018
Tax at federal statutory tax rate		21	%		21	%
State tax, net of federal benefits		3	%		0	%
Change in state effected rates		4	%		(4	)%
Tax credits, net		3	%		1	%
Change in valuation allowance		(30	)%		(17	)%
Stock-based compensation		(1	)%		(1	)%
Total		(0	)%		(0	)%

	As of December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	143,228		$	121,748
Tax credits		67,892			64,797
Liability related to sale of future royalties		35,213			26,294
Reserves and accruals		8,690			5,772
Capitalized R&D		3,949			4,614
Long-term lease liability		1,674			—
Depreciation and amortization		722			586
Other		58			—
Total noncurrent deferred tax assets		261,426			223,811
Deferred tax liabilities:
Accounting method change		(2,047	)		(2,682	)
Operating lease right-of-use assets		(1,484	)		—
Convertible notes		(12,011	)		—
Other		—			(20	)
Total noncurrent deferred tax liabilities		(15,542	)		(2,702	)
Less: Valuation allowance		(245,884	)		(221,109	)
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 our historical operating performance, reported cumulative net losses since inception, expected future losses, and difficulty in accurately forecasting our future results and an assessment of both positive and negative evidence when determining whether it is more likely than not that deferred tax assets are recoverable, we maintained a full valuation allowance on the net deferred tax assets as of December 31, 2019 and 2018. The valuation allowance increased by $24.8 million in 2019 and increased by $16.2 million in 2018.

At December 31, 2019 federal NOL carryforwards were $576.9 million and apportioned state NOL carryforwards before federal benefits were $299.5 million. If not utilized, federal and state operating loss carryforwards incurred prior to 2018 will begin to expire in various amounts beginning 2022 and 2028, respectively.

At December 31, 2019, tax credits of $64.6 million and $15.7 million for federal and state income tax purposes, respectively consisted of Research and Development Credits and Orphan Drug Credits. If not utilized, the federal carryforwards will expire in various amounts beginning in 2021. California based credit carryforwards do not expire.

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 net operating losses and tax credits to offset future taxable income. We do not believe it has experienced an ownership change since 2006, however, a portion of its NOLs and tax credits prior to 2007 will be subject to limitations under Section 382.

Activity related to our gross unrecognized tax benefits were (in thousands):

	Years Ended December 31,
	2019		2018
Balance at the beginning of the year	$	9,475	$	9,365
Decrease related to prior year tax positions		—		—
Increase related to current year tax positions		447		110
Balance at the end of the year	$	9,922	$	9,475

We are subject to income tax examination for all fiscal years since inception. Included in the balance of unrecognized tax benefits as of December 31, 2019 and 2018 are $9.1 million and $8.6 million of tax benefits, respectively, that, if recognized, would result in adjustments to other tax accounts, primarily deferred taxes.

Tax Reform

The Tax Cuts and Jobs Act of 2017 (the “Tax Act”) made significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% (the “Rate Reduction”) effective for tax years beginning after December 31, 2017. We reduced deferred tax assets at December 31, 2017 for the effect of the Rate Reduction. The Rate Reduction did not impact our provision for income taxes for 2017 due to the full valuation allowance on deferred tax assets.

Due to the complexities of implementing the provisions of the Tax Act, the staff of the U.S. Securities and Exchange Commission issued Staff Accounting Bulletin 118 (“SAB 118”), which provides guidance on accounting for tax effects of the Tax Act and permits a measurement period not to exceed one year from the enactment date for companies to complete the required analyses and accounting. As permitted under SAB 118, the adjustments we recorded due to the Tax Act, including the remeasurement of deferred tax assets and liabilities and the transition tax, were based on reasonable estimates and were considered provisional during the year. In the fourth quarter of 2018, we completed our analysis to determine the effect of the Tax Act and recorded immaterial adjustments as of December 31, 2018. The Company has considered and completed all applicable elements of tax reform under the remeasurement period.

Consolidated Statements of Operations And Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total revenues	$ 26,868	$ 31,501
Operating expenses:
Research and development	86,125	89,135
General and administrative	39,610	31,282
Total operating expenses	125,735	120,417
Operating loss	(98,867)	(88,916)
Interest expense	(6,623)	(3,797)
Non-cash interest expense on liability related to sale of future royalties	(20,737)	(17,767)
Interest and other income, net	4,535	4,191
Net loss	$ (121,692)	$ (106,289)
Net loss per share — basic and diluted	$ (2.11)	$ (1.95)
Weighted-average number of shares used in computing net loss per share — basic and diluted	57,575	54,420
Other comprehensive loss:
Unrealized gains on available-for-sale securities, net	$ 179	$ 157
Comprehensive loss	(121,513)	(106,132)
Research and Development Revenues [Member]
Revenues:
Total revenues	26,868	26,368
License Revenues [Member]
Revenues:
Total revenues	$ 0	$ 5,133

Research and Development Arrangements

12 Months Ended

Dec. 31, 2019

Research And Development [Abstract]

Research and Development Arrangements

Note 3 — Research and Development Arrangements

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

	December 31,
	2019			2018
Contract asset from the 2016 Astellas Amendment
Balance at beginning of period	$	4,554		$	9,708
Services performed		—			11,713
Cash received for services		(4,554	)		(16,867	)
Balance at end of period	$	—		$	4,554

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 $13.8 million in 2019 and $1.9 million in 2018 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 $3.3 million from Amgen as of December 31, 2019 and $1.9 million as of December 31, 2018.

Astellas Pharma Inc. (“Astellas”)

We and Astellas are parties to the Amended and Restated License and Collaboration Agreement, dated December 22, 2014, as amended (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 (the “2014 Astellas Amendment”) and expanded the objective of the collaboration to include spinal muscular atrophy (“SMA”) and potentially other neuromuscular indications for reldesemtiv and other fast skeletal muscle troponin activators (“FSTAs”). License revenues in 2018 related to our performance obligations under the 2014 Astellas Amendment. In 2018, we completed all our deliverables for the 2014 Astellas Amendment.

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

Our contract asset from the 2016 Astellas Amendment was $4.6 million as of December 31, 2018. We have completed all of our performance obligations for the 2016 Astellas Amendment as of December 31, 2019 and as a result our contract asset balance is zero as of December 31, 2019.

Currently under the Astellas Agreement, additional research and early and late state development milestone payments for research and clinical milestones, including the initiation of certain clinical studies, the submission of an application for marketing authorization for a drug candidate to certain regulatory authorities and the commercial launch of collaboration products could total over $600.0 million and includes up to $95.0 million relating to reldesemtiv in non-neuromuscular indications, and over $100.0 million related to reldesemtiv in each of SMA, ALS and other neuromuscular indications. Additionally, $200.0 million in commercial milestones could be received under the Astellas Agreement provided certain sales targets are met. We are eligible to receive up to $2.0 million in research milestone payments under the collaboration for each future potential drug candidate. We are currently in discussions with Astellas regarding amending the terms of our collaboration agreement that may lead to the reduction of payments for such research, clinical and commercial milestones. Due to the nature of drug development, including the inherent risk of development and approval of drug candidates by regulatory authorities, it is not possible to estimate if and when these milestone payments could be achieved or become due, and accordingly, are constrained and not included in the transaction price.

In the fourth quarter of 2019, Cytokinetics and Astellas agreed in principle to revise the terms of the collaboration to provide that Cytokinetics will obtain exclusive control over the development and commercialization of FSTAs, including reldesemtiv and CK-3762601. We expect to enter into definitive agreements with Astellas regarding the above agreement in principle but until we do so, the Astellas Agreement remains in effect in accordance with its current terms, the agreement in principle remains non-binding, and there can be no assurance we will enter into definitive agreements with Astellas regarding any revised terms.

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

License revenues and research and development revenues from Astellas for 2019 and 2018 were as follows (in thousands):

	Years Ended December 31,
	2019		2018
License revenues	$	—	$	5,133
Reimbursements		13,106		22,253
Milestone fees		—		2,000
	$	13,106	$	29,386

We had accounts receivable from Astellas of $1.9 million as of December 31, 2019 and $0.3 million as of December 31, 2018.

Stockholders' Equity - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding, Beginning Balance \| shares	6,454,037
Stock Options Outstanding, Granted \| shares	1,785,673
Stock Options Outstanding, Forfeited \| shares	(353,905)
Stock Options Outstanding, Ending Balance \| shares	7,759,012
Stock Options Outstanding, Exercisable \| shares	5,349,164
Weighted Average Exercise Price per Share, Beginning Balance \| $ / shares	$ 8.72
Weighted Average Exercise Price per Share, Granted \| $ / shares	8.41
Weighted Average Exercise Price per Share, Exercised \| $ / shares	7.78
Weighted Average Exercise Price per Share, Forfeited \| $ / shares	10.44
Weighted Average Exercise Price per Share, Ending Balance \| $ / shares	8.59
Weighted Average Exercise Price per Share, Exercisable \| $ / shares	$ 8.57
Weighted Average Remaining Contractual Life	6 years 6 months
Weighted Average Remaining Contractual Life, Exercisable at December 31, 2019	5 years 7 months 6 days
Aggregate Intrinsic Value \| $	$ 18.8
Aggregate Intrinsic Value, Exercisable at December 31, 2019 \| $	$ 13.2
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding, Exercised \| shares	(126,793)

Organization and Accounting Policies - Additional Information (Detail) $ in Thousands		12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2019 USD ($) Financial_Institution Obligation	Dec. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit incurred		$ (865,016)	$ (743,324)
Net loss		(121,692)	(106,289)
Net cash provided by (used in) operating activities		(90,907)	(101,215)
Cash, cash equivalents and investments		$ 267,800	198,700
Cash requirements term		12 months
Number of major financial institutions \| Financial_Institution		2
Lease expiration year		2021
Lease, practical expedients, package		true
Contract assets		$ 0	4,554
Contract liabilities		0	$ (18,750)
Without Adoption of ASU 2019-12 [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred tax benefit		$ 12,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Contract assets	$ 16,700
Contract liabilities	7,700
Decrease in accumulated deficit	$ 9,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of performance obligation \| Obligation		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] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives		3 years
Leasehold Improvements [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives		7 years

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (121,692)	$ (106,289)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense on liability related to sale of future royalties	20,737	17,767
Non-cash stock-based compensation expense	10,759	9,761
Depreciation and amortization of property and equipment	1,293	1,239
Interest receivable and amortization on investments	(2,587)	(1,677)
Non-cash interest expense related to debt	919	920
Changes in operating assets and liabilities:
Accounts receivable	(2,932)	(1,119)
Contract assets	4,554	5,154
Prepaid and other assets	(3,862)	1,817
Operating lease right-of-use assets	3,552	0
Accounts payable	4,396	(1,490)
Accrued and other liabilities	(2,168)	(2,063)
Contract liabilities	0	(18,750)
Operating lease liabilities	(3,876)	0
Deferred revenue	0	(6,485)
Net cash used in operating activities	(90,907)	(101,215)
Cash flows from investing activities:
Purchases of investments	(277,883)	(240,224)
Sales and maturities of investments	205,795	246,232
Purchases of property and equipment	(2,619)	(889)
Sales of property and equipment	0	14
Net cash provided by (used in) investing activities	(74,707)	5,133
Cash flows from financing activities:
Issuance of common stock under at the market offering, net of issuance costs	36,214	0
Proceeds from stock-based award activities, net	1,393	3,234
Net proceeds from long-term debt, net of debt discount and issuance costs	1,710	9,898
Net proceeds from convertible notes, net of debt discount and issuance costs	133,860	0
Purchase of capped call options associated with convertible notes	(13,386)	0
Net cash provided by financing activities	159,791	13,132
Net decrease in cash and cash equivalents	(5,823)	(82,950)
Cash and cash equivalents, beginning of period	42,256	125,206
Cash and cash equivalents, end of period	36,433	42,256
Supplemental cash flow disclosures:
Cash paid for interest	4,059	2,877
Right-of-use assets recognized in exchange for lease obligations	10,687	0
Issuance of warrants in connection with long-term debt	$ 185	$ 182

Debt - Additional Information (Detail)			12 Months Ended
Debt - Additional Information (Detail)	Nov. 13, 2019 USD ($) $ / shares shares	Nov. 07, 2019 $ / shares	Dec. 31, 2019 USD ($) Installment Day	Dec. 31, 2018 USD ($)	May 17, 2019 USD ($)
Debt Instrument [Line Items]
Interest expense			$ 6,623,000	$ 3,797,000
Net proceeds from convertible notes, net of debt discount and issuance costs			133,860,000	0
Purchase of capped call options associated with convertible notes			13,386,000	0
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			$ 5,200,000	$ 3,800,000
Stated interest rate on the amounts borrowed under the Agreement			8.57%
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 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 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 is repayable in monthly interest-only payments through December 31, 2020. The interest only period may be extended for six or twelve months if both of the following milestones occur: (i) specified events related to the development of (a) reldesemtiv, a novel fast skeletal muscle troponin activator, in spinal muscular atrophy or amyotrophic lateral sclerosis, or (b) CK-3773274, a novel cardiac myosin inhibitor, in cardiomyopathy; and/or (ii) specified results from GALACTIC-HF, a Phase 3 trial of omecamtiv mecarbil, a novel cardiac myosin activator. 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 130% of the conversion price on each applicable trading day; (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			$ 3,100,000
Unamortized debt issuance cost			$ 50,700,000
Unamortized debt discount amortization period			7 years
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			130.00%
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

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

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

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

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

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

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

Fair Value of Financial Assets

	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

	December 31, 2018
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	Level 1	$	34,771	$	—	$	—		$	34,771
U.S. Treasury securities	Level 1		56,999		—		(41	)		56,958
Agency bonds	Level 2		61,792		1		(14	)		61,779
Commercial paper	Level 2		19,448		—		(13	)		19,435
Corporate obligations	Level 2		17,644		2		(8	)		17,638
		$	190,654	$	3	$	(76	)	$	190,581

Interest income was $4.5 million and $4.2 million in 2019 and 2018, respectively. Investments available for sale at December 31, 2019 and 2018 exclude an investment in equity classified as a Level 1 investment in our short-term investments with a fair value of $1.0 million and $0.7 million, respectively, and unrealized gain of $0.3 million and $0.1 million, respectively. At December 31, 2019, there were no investments that had been in a continuous unrealized loss position for 12 months or longer, none of the investments were other-than-temporarily impaired, unrealized losses were not due to changes in credit risk and we believe investments with an unrealized loss would be held until maturity.

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 December 31, 2019 and 2018, the fair value of our term loan approximated its carrying value of $45.1 million and $42.4 million, respectively, because it is carried at a market observable interest rate, which is a Level 2 input (see Note 7 – “Debt”).

As of December 31, 2019, the estimated fair value of our convertible notes was $170.6 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 December 31, 2019 and 2018, 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

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Provision for income tax	$ 0
Increase (decrease) in valuation allowance	$ 24,800,000	$ 16,200,000
Research and development credits and orphan drug credits, federal carryforwards will expire	2021
Unrecognized tax benefits	$ 9,100,000	$ 8,600,000
Effective tax rate	21.00%	21.00%	34.00%
Tax Cuts and Jobs Act, maximum measurement period permitted for companies to complete accounting	1 year
Federal Tax [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 576,900,000
Net operating loss carryforwards expiration	2022
Credit carryforwards for federal and state	$ 64,600,000
Federal and State Tax [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 299,500,000
Net operating loss carryforwards expiration	2028
Credit carryforwards for federal and state	$ 15,700,000

Stockholders' Equity - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Restricted Stock Units, Beginning Balance \| shares	546,500
Number of Restricted Stock Units, Granted \| shares	607,150
Number of Restricted Stock Units, Released \| shares	(266,500)
Number of Restricted Stock Units, Forfeited \| shares	(48,075)
Number of Restricted Stock Units, Ending Balance \| shares	839,075
Weighted Average Award Date Fair Value per Share, Beginning Balance \| $ / shares	$ 8.53
Weighted Average Award Date Fair Value per Share, Granted \| $ / shares	7.14
Weighted Average Award Date Fair Value per Share, Released \| $ / shares	8.84
Weighted Average Award Date Fair Value per Share, Forfeited \| $ / shares	7.34
Weighted Average Award Date Fair Value per Share, Ending Balance \| $ / shares	$ 7.49

Stockholders' Equity - Fair Value of Share-Based Payments was Estimated on Date of Grant Based on Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Options [Member]
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Risk-free interest rate, minimum	1.60%	2.30%
Risk-free interest rate, maximum	3.00%	3.00%
Volatility, minimum	73.00%	73.00%
Volatility, maximum	76.00%	74.00%
Expected term in years	6 years 6 months	6 years 6 months
Expected dividend yield	0.00%	0.00%
ESPP [Member]
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Risk-free interest rate, minimum	1.80%	1.50%
Risk-free interest rate, maximum	2.40%	2.50%
Volatility, minimum	73.00%	73.00%
Volatility, maximum	76.00%	74.00%
Expected term in years	7 months 6 days	6 months
Expected dividend yield	0.00%	0.00%

Leases - Schedule of Undiscounted Future Non-cancellable Lease Payments under the Lease Agreements (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Leases [Abstract]
2020	$ 5,240
2021	4,616
2022	12,694
2023	16,195
2024	16,648
Thereafter	170,919
Total undiscounted future lease payments	226,312
Less: Undiscounted lease payments related to Expansion Lease	(1,335)
Less: Undiscounted lease payments related to Oyster Point Lease	(217,667)
Less: Present value adjustments	(499)
Total lease liability	$ 6,811

Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Interest Income	$ 4,500,000	$ 4,200,000
Available for sale investments, fair value	1,000,000	700,000
Available for sale investments, unrealized gain	300,000	100,000
Available for sale investments in continous unrealized loss position for 12 months or longer	0
Long-term debt, fair value	45,100,000	$ 42,400,000
Convertible debt, fair value	170,600
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

Debt - Schedule of Future Minimum Payments under Term Loan Agreement (Detail) - Term Loan Agreement [Member] - Oxford and Silicon Valley Bank [Member] $ in Thousands	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
2020	$ 3,921
2021	18,312
2022	17,009
2023	20,291
Future minimum payments	59,533
Long-term debt, alternative
Future minimum payments	59,533
Less: Interest and final payment	(14,533)
Term Loan, gross	$ 45,000

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
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	163,000,000
Common stock, shares issued	59,172,124	54,717,906
Common stock, shares outstanding	59,172,124	54,717,906

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	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 264,265	$ 190,654
Unrealized Gains	123	3
Unrealized Losses	(17)	(76)
Fair Value	264,371	190,581
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	31,535	34,771
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	31,535	34,771
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	134,845	56,999
Unrealized Gains	72	0
Unrealized Losses	(1)	(41)
Fair Value	134,916	56,958
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	47,024	61,792
Unrealized Gains	23	1
Unrealized Losses	(9)	(14)
Fair Value	47,038	61,779
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	10,435	19,448
Unrealized Gains	4	0
Unrealized Losses	0	(13)
Fair Value	10,439	19,435
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	40,426	17,644
Unrealized Gains	24	2
Unrealized Losses	(7)	(8)
Fair Value	$ 40,443	$ 17,638

Organization and Accounting Policies - Summary of Impact on Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Short-term lease liability	$ (4,616)		$ 0
Long-term lease liability	$ (2,195)		$ (771)
ASC 840 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred rent classified as accrued liabilities		$ (323)
Deferred rent classified as other long-term liabilities		(773)
Short-term lease liability		0
Long-term lease liability		0
Operating lease right-of-use assets and other assets		0
ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred rent classified as accrued liabilities		0
Deferred rent classified as other long-term liabilities		0
Short-term lease liability		(4,460)
Long-term lease liability		(6,227)
Operating lease right-of-use assets and other assets		9,591
Impact of Adoption [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred rent classified as accrued liabilities		323
Deferred rent classified as other long-term liabilities		773
Short-term lease liability		(4,460)
Long-term lease liability		(6,227)
Operating lease right-of-use assets and other assets		$ 9,591

Net Loss Per Share - Instruments Excluded from the Computation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	25,465	6,246
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	7,759	5,476
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	165	116
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	839	547
Shares Issuable Related to the ESSP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	27	107
Shares Issuable Upon Conversion of Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares	16,675	0

Research and Development Arrangements - Summary of License Revenues and Research and Development Revenues (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	$ 26,868	$ 31,501
Astellas [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	13,106	29,386
License Revenues [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	0	5,133
License Revenues [Member] \| Astellas [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	0	5,133
Reimbursements [Member] \| Astellas [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	13,106	22,253
Milestone Fees [Member] \| Astellas [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	$ 0	$ 2,000

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Depreciation expense	$ 1.3	$ 1.2
Employer contributions under the plan	$ 0.6	$ 0.5

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued liabilities:
Clinical and preclinical costs	$ 2,215	$ 8,618
Compensation related	8,343	6,118
Other accrued expenses	1,565	1,021
Total accrued liabilities	$ 12,123	$ 15,757

Research and Development Arrangements - Schedule of Changes in Contract Assets and Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Balance at beginning of period	$ 4,554
Balance at end of period	0	$ 4,554
2016 Astellas Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Balance at beginning of period	4,554	9,708
Services performed	0	11,713
Cash received for services	(4,554)	(16,867)
Balance at end of period	$ 0	$ 4,554

Liability Related to Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2017	Dec. 31, 2019	Dec. 31, 2018
Liability Related to Sale of Future Royalties [Line Items]
Non-cash interest expense recognized		$ 20,737	$ 17,767
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		$ 20,700	$ 17,800