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Nature of Operations - Additional Information (Detail)	12 Months Ended
Nature of Operations - Additional Information (Detail)	Dec. 31, 2019 Segment
Accounting Policies [Abstract]
Number of operating segment	1

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 15,369	$ 31,213
Short-term investments	61,496	88,914
Restricted cash		50
Accounts receivable	15,000
Prepaid and other current assets	4,201	3,814
Total current assets	96,066	123,991
Other assets, noncurrent	257	543
Right-of-use assets	1,927
Property and equipment, net of $0.4 million and $0.3 million of accumulated depreciation in 2019 and 2018, respectively	304	386
Total assets	98,554	124,920
Current liabilities:
Accounts payable	4,279	1,248
Accrued compensation	2,106	1,495
Deferred revenue	15,000
Other accrued liabilities	7,031	2,043
Operating lease liability	483
Deferred rent, current portion		15
Total current liabilities	28,899	4,801
Operating lease liability, noncurrent	1,319
Deferred rent, noncurrent portion		174
Total liabilities	30,218	4,975
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized; zero shares issued and outstanding
Common stock, $0.001 par value, 100,000,000 shares authorized; 12,040,835 and 11,954,528 shares issued and outstanding at December 31, 2019 and 2018, respectively	12	12
Additional paid-in capital	326,810	323,279
Accumulated other comprehensive income (loss)	34	(4)
Accumulated deficit	(258,520)	(203,342)
Total stockholders’ equity	68,336	119,945
Total liabilities and stockholders’ equity	$ 98,554	$ 124,920

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (55,178)	$ (30,055)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale debt securities	38	(4)
Total comprehensive loss	$ (55,140)	$ (30,059)

- Definition

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

+ References + Details

Fair Values of Stock Options Estimated Using Black-Scholes Valuation Model (Detail) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Expected term (in years)	5 years 11 months 23 days	6 years 14 days
Risk-free interest rate	2.35%	2.67%
Dividend yield	0.00%	0.00%
Volatility	90.81%	92.61%
Weighted-average fair value of stock options granted	$ 5.85	$ 9.97

Consolidated Statements of Cash Flows (Parenthetical) - USD ($)
$ in Thousands

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Statement Of Cash Flows [Abstract]

Cash and cash equivalents

$ 15,369

$ 31,213

Restricted cash

Total cash and restricted cash

$ 15,369

^[1]

$ 31,263

^[1]

$ 19,805

[1]	(a) The following table provides a reconciliation of cash and restricted cash to amounts reported within the consolidated balance sheets:

Subsequent Event - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Feb. 13, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Common stock, shares issued		12,040,835	11,954,528
Subsequent Event
Subsequent Event [Line Items]
Common stock, shares issued	5,307,692
Sale of stock price per share	$ 6.50
Underwriting discounts and offering expenses	$ 32.0

Schedule of Supplemental Cash Flow Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Cash paid for leases that were included in operating cash outflows	$ 562

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

7.	Commitments and Contingencies

Manufacturing Agreements

On May 20, 2016, the Company signed a development and manufacturing services agreement with AGC Biologics, Inc. (“AGC”), formerly known as CMC ICOS Biologics, Inc., pursuant to which AGC will conduct manufacturing development of agreed upon product candidates. The Company had firm work orders with AGC to manufacture MarzAA and DalcA to support its clinical trials totaling $12.4 million at December 31, 2019 and the payment obligations remaining was $4.6 million.

On October 9, 2019, the Company and Catalent Indiana, LLC (“Catalent”) signed a clinical supply services agreement, effective October 4, 2019, pursuant to which Catalent will conduct drug product development of agreed upon product candidates. The Company currently has firm work orders with Catalent to manufacture DalcA to support its clinical trial totaling $0.5 million and the payment obligations remaining at December 31, 2019 was $0.4 million.

Collaborative Agreements

The Company has committed to make potential future sublicense, milestone, and royalty payments to collaborative partners as part of licensing and development programs. The Company is unable to determine precisely when and if its payment obligations under the agreements will become due as these obligations are based on uncertain events, the achievement of which is subject to a significant number of risks and uncertainties. Because it is uncertain if and when these milestones will be achieved, such contingencies are not recorded until become probable. See Note 8.

Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net loss	$ (55,178)	$ (30,055)
Weighted-average number of shares used in computing net loss per share, basic and diluted	12,004,489	11,213,884
Net loss per share, basic and diluted	$ (4.60)	$ (2.68)

Summary of Stock-Based Compensation Recognized (Detail) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]

Total stock-based compensation

$ 3,204

$ 2,606

Research and development

Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]

Total stock-based compensation

1,052

606

General and Administrative

Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]

Total stock-based compensation

^[1]

$ 2,152

$ 2,000

[1]

Included $0.03 and $0.1 million related to modifications of certain Board member stock options in the years ended December 31, 2019 and 2018, respectively. These modifications extended the post-termination exercise period of certain options. Also included in general and administrative stock-based compensation for the year ended December 31, 2019 and 2018 is expense related to 24,235 and 6,790 shares of common stock issued to certain board members in lieu of their cash compensation, respectively.

Subsequent Event

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent Event

16.	Subsequent Event

In February 2020, the Company sold an aggregate of 5,307,692 registered shares of common stock at $6.50 per share, for net proceeds, after deducting underwriting discounts and offering expenses, of approximately $32.0 million.

Related Parties - Additional Information (Detail) - Mosaic - Intravitreal Anti-Complement Factor 3 - USD ($) $ in Millions		12 Months Ended
	Jan. 10, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event
Related Party Transaction [Line Items]
Payment related to collaboration	$ 3.0
Collaboration Agreement
Related Party Transaction [Line Items]
Expenses related to collaboration		$ 1.1	$ 1.3
Biogen Collaboration \| Subsequent Event
Related Party Transaction [Line Items]
Upfront license fee received from collaboration agreement	$ 15.0

Anti-dilutive Security not Included In Diluted per Share Calculations (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,585,398	1,372,171
Options To Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,577,541	1,361,977
Common Stock Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	7,857	10,194

Net Loss per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Net Loss per Share Attributable to Common Stockholders

15.	Net Loss per Share Attributable to Common Stockholders

The following table sets forth the computation of the basic and diluted net loss per common share during the years ended December 31, 2019 and 2018 (in thousands, except share and per share data):

	Year Ended December 31,
	2019			2018
Net loss	$	(55,178	)	$	(30,055	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		12,004,489			11,213,884
Net loss per share, basic and diluted	$	(4.60	)	$	(2.68	)

Since the Company was in a loss position for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods as the inclusion of all potential common shares outstanding would have been anti-dilutive. Potentially dilutive securities on an as-if converted basis that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	Year Ended December 31,
	2019		2018
Options to purchase common stock		1,577,541		1,361,977
Common stock warrants		7,857		10,194
Total		1,585,398		1,372,171

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jun. 13, 2018	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Stock options granted		450,900	612,050
Number of common stock available for future grant		1,014,126
Number of shares of common stock issued to certain board members in lieu of cash compensation		24,235	6,790
Shares remaining outstanding		1,577,541
Stock-based compensation expense		$ 3,204	$ 2,606
Employee Stock Option
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Expected term of stock options		5 years 11 months 23 days	6 years 14 days
Unrecognized employee stock based compensation expense		$ 5,300
Unrecognized employee stock based compensation expense, period for recognition		2 years 4 months 28 days
2018 Employee Stock Purchase Plan
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Number of common stock available for future grant		218,692
Number of common stock authorized for issuance		239,545
Number of common stock stock issued		20,853
Stock-based compensation expense		$ 100	$ 30
2018 Omnibus Incentive Plan
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Number of common stock available for future grant	1,500,000
2018 Employee Stock Purchase Plan
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Maximum employee subscription rate	15.00%
2018 Employee Stock Purchase Plan \| Maximum
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Percentage of fair market value of common stock	85.00%

Reconciliation of Statutory Federal Income Tax (benefit) Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax at statutory federal rate	(21.00%)	(21.00%)
State Tax (benefit)—net of federal benefit	(0.06%)	(0.03%)
Permanent differences	0.43%	0.68%
Tax credits	(11.20%)	(0.76%)
Derecognition due to Sec. 382 and 383 limitations	(0.00%)	(20.16%)
Change in valuation allowance	31.20%	39.33%
Other	0.63%	1.94%
Effective tax rate	0.00%	0.00%

Components of the Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Accruals and reserves	$ 936	$ 751
Net operating loss carry forwards	34,392	23,559
Tax credit carry forwards	9,945	3,772
Fixed and intangible assets	10	3
Valuation allowance	$ (45,283)	$ (28,085)

Summary of Present Value Assumptions used in Calculating Present Value of Lease Payments (Detail)	Dec. 31, 2019
Lessee Disclosure [Abstract]
Weighted-average remaining lease term	3 years 3 months 29 days
Weighted-average discount rate	6.00%

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Feb. 15, 2018	Feb. 13, 2018	Apr. 12, 2017	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017
Stockholders Equity Disclosure [Line Items]
Preferred stock, shares issued				0	0
Preferred stock, shares outstanding				0	0
Net proceeds from sale of common stock	$ 106.8
Warrants to purchase common stock			2,070,000
Warrants exercise price			$ 5.50	$ 155.73	$ 53.61	$ 6.46
Proceeds allocated to warrants, net			$ 5.0
Number of warrants outstanding				10,194	7,857	1,751,708
April 2017 Underwritten Public Offering
Stockholders Equity Disclosure [Line Items]
Number of warrants outstanding					0
Convertible Preferred Stock
Stockholders Equity Disclosure [Line Items]
Conversion of preferred stock to common stock, shares				(3,680)
Common Stock
Stockholders Equity Disclosure [Line Items]
Conversion of preferred stock to common stock, shares				736,000
Firm commitment underwritten public offering shares		2,941,176
Issuance of stock, shares	3,382,352
Common stock price, per share	$ 34.00
Common Stock \| Overallotment Option
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	441,176

Stock Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Based Compensation

10.	Stock Based Compensation

2018 Omnibus Incentive Plan

In June 2018, stockholders of the Company approved the Company’s 2018 Omnibus Incentive Plan (the “2018 Plan”). The 2018 Plan had previously been approved by the Company’s Board of Directors (the “Board”) and the Compensation Committee of the Board, subject to stockholder approval. The 2018 Plan became effective on June 13, 2018 and provided an additional 1,500,000 stock options, following receipt of the requisite stockholder approval. The 2018 Plan replaces the Company’s 2015 Stock Incentive Plan, as amended (the “2015 Plan”). All awards outstanding under the 2015 Plan will remain in effect in accordance with their respective terms.

The following table summarizes stock option activity under the Company’s equity incentive plans and related information:

	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (thousands)
Outstanding — December 31, 2017		821,741		$	13.69		9.17	$	6,376
Options granted		612,050		$	13.13
Options exercised		(12,716	)	$	4.17			$	213
Options canceled/forfeited		(43,315	)	$	7.76
Options expired		(15,783	)	$	158.81
Outstanding — December 31, 2018		1,361,977		$	12.04		8.71	$	2,294
Options granted		450,900		$	7.85
Options exercised		(41,219	)	$	4.57			$	159
Options forfeited		(182,722	)	$	8.36
Options expired		(11,395	)	$	96.49
Outstanding — December 31, 2019		1,577,541		$	10.85		8.15	$	1,350
Exercisable — December 31, 2019		740,356		$	13.30
Shares available to be granted — December 31, 2019		1,014,126

Valuation Assumptions

The Company estimated the fair value of stock options granted using the Black-Scholes option-pricing formula and a single option award approach. Due to its limited history as a public company and limited number of sales of its common stock, the Company estimated its volatility considering a number of factors including the use of the volatility of comparable public companies. The expected term of options granted under the Plan, all of which qualify as “plain vanilla” per SEC Staff Accounting Bulletin 107, is determined based on the simplified method due to the Company’s limited operating history and is 5.98 years based on the average between the vesting period and the contractual life of the option. The risk-free rate is based on the yield of a U.S. Treasury security with a term consistent with the option. This fair value is being amortized ratably over the requisite service periods of the awards, which is generally the vesting period.

The fair value of employee stock options was estimated using the following weighted-average assumptions for the year ended December 31, 2019 and 2018:

	Year Ended December 31,
	2019			2018
Employee Stock Options:
Expected term (in years)		5.98			6.04
Risk-free interest rate		2.35	%		2.67	%
Dividend yield		—			—
Volatility		90.81	%		92.61	%
Weighted-average fair value of stock options granted	$	5.85		$	9.97

Total stock-based compensation recognized was as follows (in thousands):

	Year Ended December 31,
	2019		2018
Research and development	$	1,052	$	606
General and administrative⁽¹⁾		2,152		2,000
Total stock-based compensation	$	3,204	$	2,606

(1)	Included $0.03 and $0.1 million related to modifications of certain Board member stock options in the years ended December 31, 2019 and 2018, respectively. These modifications extended the post-termination exercise period of certain options.

Also included in general and administrative stock-based compensation for the year ended December 31, 2019 and 2018 is expense related to 24,235 and 6,790 shares of common stock issued to certain board members in lieu of their cash compensation, respectively.

As of December 31, 2019, 1,014,126 shares of common stock were available for future grant and 1,577,541 options to purchase shares of common stock were outstanding. As of December 31, 2019, the Company had unrecognized employee stock-based compensation expense of $5.3 million, related to unvested stock option awards, which is expected to be recognized over an estimated weighted-average period of 2.41 years.

2018 Employee Stock Purchase Plan

In June 2018, the Company’s stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”). The ESPP had previously been approved by the Board and the Compensation Committee of the Board, subject to stockholder approval which became effective as of June 13, 2018. Under the ESPP, employees meeting certain specific employment qualifications are eligible to participate and can purchase shares of common stock semi-annually on February 9^th and August 9^th of each year, through payroll deductions. The purchase price is 85% of the lower of the fair market value of the stock at the commencement or end of the offering period. The ESPP permits eligible employees to purchase shares of common stock through payroll deductions for up to 15% of qualified compensation.

The Company’s ESPP is subject to an Evergreen provision which shares may be added to the pool as needed. As of December 31, 2019, a total of 239,545 shares of common stock may be granted in accordance with the terms of the ESPP. As of December 31, 2019, 20,853 shares of common stock have been issued to employees participating in the ESPP and 218,692 shares are available for issuance under the ESPP. Compensation expense, using Black-Scholes, for the ESPP was $0.1 million and $0.03 million as of December 31, 2019 and 2018, respectively, and is included in stock-based compensation expense.

Summary of Maturity of Operating Lease Liabilities - (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2020	$ 578
2021	596
2022	613
2023	209
Total undiscounted lease payments	1,996
Less: imputed interest	(194)
Total operating lease liability	1,802
Total operating lease liability	1,802
Less: current portion of operating lease liability	483
Operating lease liability, noncurrent	$ 1,319

Financial Instruments

12 Months Ended

Dec. 31, 2019

Investments All Other Investments [Abstract]

Financial Instruments

5.	Financial Instruments

Cash equivalents, restricted cash and short-term investments, which are classified as available-for-sale securities, consisted of the following (in thousands):

December 31, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	15,369	$	—	$	—	$	15,369
U.S. government agency securities		51,467		23		—		51,490
Federal agency securities		9,995		11		—		10,006
Total financial assets	$	76,831	$	34	$	—	$	76,865
Classified as:
Cash and cash equivalents							$	15,369
Short-term investments								61,496
							$	76,865

December 31, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	29,090	$	—	$	—		$	29,090
Federal agency securities (cash equivalents)		999		—	$	—			999
Restricted cash		50		—		—			50
U.S. government agency securities		74,144		1		(6	)		74,139
Federal agency securities		14,774		1		—			14,775
Total financial assets	$	119,057	$	2	$	(6	)	$	119,053
Classified as:
Cash and cash equivalents								$	30,089
Short-term investments									88,914
Restricted cash									50
								$	119,053

As of December 31, 2019, the remaining contractual maturities of available-for-sale debt securities was less than one year. There have been no material realized gains or losses on available-for-sale debt securities for the periods presented. The carrying amounts of cash, other assets, accounts receivable, accounts payable and other payables approximate their fair values due to the short-term maturity of these instruments.

Interest and Other Income, Net

12 Months Ended

Dec. 31, 2019

Other Income And Expenses [Abstract]

Interest and Other Income, Net

13.	Interest and Other Income, Net

The following table shows the detail of interest and other income, net for the years ended December 31, 2019 and 2018 (in thousands):

	Year Ended December 31,
	2019			2018
Interest income	$	2,145		$	2,229
Dividend income		—			4
Miscellaneous (expense) income⁽¹⁾		(39	)		1,650
Loss on disposal of property and equipment		—			(116	)
Other		(7	)		—
Total interest and other income, net	$	2,099		$	3,767

(1)	$1.7 million miscellaneous income for the year ended December 31, 2018 is mainly composed of a $1.5 million milestone payment received under an agreement associated with neuronal nicotinic receptor (“NNR”) assets sold in 2016.

Other Accrued Liabilities

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Other Accrued Liabilities

6.	Other Accrued Liabilities

Other accrued liabilities consisted of the following (in thousands):

	Year Ended December 31,
	2019		2018
Manufacturing	$	4,320	$	1,012
Professional and consulting services		2,026		597
Clinical		435		234
Other		250		200
Total other accrued liabilities	$	7,031	$	2,043

Summary of Stock-Based Compensation Recognized (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,204	$ 2,606
Board Member Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 30	$ 100

Assets and Liabilities Measured at Fair Value (Parenthetical) (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Collateral for Corporate Credit Card
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash	$ 50

Net Loss per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Basic and Diluted Net Loss Per Common Share

The following table sets forth the computation of the basic and diluted net loss per common share during the years ended December 31, 2019 and 2018 (in thousands, except share and per share data):

	Year Ended December 31,
	2019			2018
Net loss	$	(55,178	)	$	(30,055	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		12,004,489			11,213,884
Net loss per share, basic and diluted	$	(4.60	)	$	(2.68	)

Anti-dilutive Security not Included In Diluted per Share Calculations

	Year Ended December 31,
	2019		2018
Options to purchase common stock		1,577,541		1,361,977
Common stock warrants		7,857		10,194
Total		1,585,398		1,372,171

Financial Instruments - Additional Information (Detail)	12 Months Ended
Financial Instruments - Additional Information (Detail)	Dec. 31, 2019 USD ($)
Financial Instrument [Line Items]
Material realized gains or losses on available-for-sale securities	$ 0
Maximum
Financial Instrument [Line Items]
Available for sale debt securities contractual maturities	1 year

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2019	Feb. 07, 2020	Jun. 30, 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	CBIO
Entity Registrant Name	Catalyst Biosciences, Inc.
Entity Central Index Key	0001124105
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 Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		12,076,777
Entity Public Float			$ 86,980,239
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity File Number	000-51173
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	56-2020050
Entity Address, Address Line One	611 Gateway Blvd
Entity Address, Address Line Two	Suite 710
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	871-0761
Document Annual Report	true
Document Transition Report	false

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Reconciliation of Federal Income Tax Rate to Company's Effective Tax Rate

The reconciliation of the federal statutory income tax rate to the Company’s effective tax rate for the years ended December 31, 2019 and 2018 are as follows:

	Year Ended December 31,
	2019			2018
Tax at statutory federal rate		-21.00	%		-21.00	%
State Tax (benefit)—net of federal benefit		-0.06	%		-0.03	%
Permanent differences		0.43	%		0.68	%
Tax credits		-11.20	%		-0.76	%
Derecognition due to Sec. 382 and 383 limitations		0.00	%		-20.16	%
Change in valuation allowance		31.20	%		39.33	%
Other		0.63	%		1.94	%
Effective tax rate		0.00	%		0.00	%

Components of the Company's Deferred Tax Assets (Liabilities)

Significant components of the Company’s deferred tax assets as of December 31, 2019 and 2018 consist of the following (in thousands):

	Year Ended December 31,
	2019			2018
Deferred tax assets:
Accruals and reserves	$	936		$	751
Net operating loss carry forwards		34,392			23,559
Tax credit carry forwards		9,945			3,772
Fixed and intangible assets		10			3
Valuation allowance		(45,283	)		(28,085	)
Net deferred tax assets:	$	—		$	—

Unrecognized Tax Benefits

A reconciliation of the beginning and ending balance of the unrecognized tax benefits is as follows (in thousands):

Beginning Balance at January 1, 2018	$	1,475
Increase/(Decrease) of unrecognized tax benefits taken in prior years		13
Increase/(Decrease) of unrecognized tax benefits related to current year		85
Ending Balance at December 31, 2018	$	1,573
Increase/(Decrease) of unrecognized tax benefits taken in prior years		45
Increase/(Decrease) of unrecognized tax benefits related to current year		253
Ending Balance at December 31, 2019	$	1,871

Collaborations

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaborations

12.	Collaborations

Pfizer

In 2009, the Company licensed MarzAA to Wyeth Pharmaceuticals, Inc. (Wyeth). Wyeth was subsequently acquired by Pfizer who terminated the license and collaboration agreement after completing an IV Phase 1 trial. Pursuant to the collaboration termination agreement entered on December 8, 2016, in exchange for the rights to certain Pfizer technology, the Company agreed to make contingent cash payments to Pfizer in an aggregate amount equal to up to $17.5 million, payable upon the achievement of clinical, regulatory and commercial milestones. Following commercialization of any covered product, Pfizer would also receive a single-digit royalty on net product sales on a country-by-country basis for a predefined royalty term. In February 2018, the Company paid Pfizer a $1.0 million milestone payment based on the dosing of the first patient in the ongoing Phase 2 study; the amount was recorded as a research and development expense for the year ended December 31, 2018. No additional payments were made to Pfizer for the year ended December 31, 2019.

ISU Abxis

The Company collaborated with ISU Abxis (ISU), in the early development of DalcA. Under the collaboration agreement, ISU conducted the Phase I clinical trial of DalcA and was responsible for all manufacturing activities for the Phase 1 clinical trial. In December 2018, the Company entered into an amended and restated license agreement with ISU (the “A&R ISU Abxis Agreement”), which amended and restated its previous license and collaboration agreement with ISU previously entered into in September 2013, as subsequently amended in October 2014 and December 2016 (the “Original ISU Abxis Agreement”). Under the A&R ISU Abxis Agreement, ISU will receive commercialization rights in South Korea to the Company’s engineered Factor IX dalcinonacog alfa - DalcA and the Company will receive clinical development and commercialization rights in the rest of world (excluding South Korea) and manufacturing development and manufacturing rights worldwide (including South Korea). The A&R ISU Abxis Agreement eliminates the profit-sharing arrangement in the Original ISU Abxis Agreement and provides for a low single-digit royalty payment to ISU, on a country-by-country basis, for net product sales of DalcA by the Company or its affiliates in each country other than South Korea. Pursuant to the A&R ISU Abxis Agreement, the Company will also pay up to an aggregate of $19.5 million in milestone payments to ISU, inclusive of $2.5 million in regulatory and development milestone payments and up to $17.0 million in commercial milestone payments, if the applicable milestones are met. As of December 31, 2019, the milestones have not been met.

Biogen

On December 18, 2019, the Company and Biogen International GmbH (“Biogen”) entered into a License and Collaboration Agreement (the “Biogen Agreement”), under which the Company granted Biogen a worldwide, royalty-bearing, exclusive, sublicenseable license (“Exclusive License”) to develop and commercialize CB 2782-PEG and other anti-C3 proteases for potential treatment of dry AMD and other retinal disorders. Pursuant to the Biogen Agreement, the Company will perform certain pre-clinical and manufacturing activities (“Research Services”), and Biogen will be solely responsible for funding the pre-clinical and manufacturing activities and performing IND-enabling activities, worldwide clinical development, and commercialization. The Company will provide the Research Services over a term of thirty months with Biogen having the option to extend the term for two additional twelve-month periods.

Under the terms of the Biogen Agreement, the Company received an up-front payment for the transfer of the Exclusive License (inclusive of certain know-how) of $15.0 million in January 2020. The Company is eligible to receive development milestones and sales milestones of up to $340.0 million. In addition, the Company is eligible to receive royalties in the range of single-digit to low double-digit percentage rates of annual net sales on a product-by-product and country-by-country basis. The Company will also receive reimbursements for costs associated with the performance of the Research Services.

The Company determined that the performance obligations under the Biogen Agreement were the Exclusive License and the Research Services. For the Exclusive License, the Company used the residual approach in determining the standalone selling price SSP, which includes the upfront payments, milestones and royalties. For the Research Services, the Company used the historical pricing approach for determining the SSP, which includes the reimbursement of personnel and out-of-pocket costs.

The Biogen Agreement will continue on a product-by-product and country-by-country basis until the tenth anniversary of the first commercial sale of the first product in a country, unless being early terminated by either party as specified under the agreement.

As of December 31, 2019, the Company recorded $15.0 million in accounts receivable and deferred revenue for the Exclusive License. The deferred revenue has been recognized in revenue in 2020 upon the transfer of the Exclusive License and the related know-how.

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Property and equipment, net, accumulated depreciation	$ 0.4	$ 0.3
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	12,040,835	11,954,528
Common stock, shares outstanding	12,040,835	11,954,528

Consolidated Statements of Cash Flows - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Operating Activities

Net loss

$ (55,178)

$ (30,055)

Adjustments to reconcile net loss to net cash used in operating activities:

Stock-based compensation expense

3,204

2,606

Depreciation and amortization

146

149

Loss on disposal of property and equipment

116

Changes in operating assets and liabilities:

Accounts receivable

(15,000)

Prepaid and other assets

(490)

(2,895)

Accounts payable

3,031

500

Accrued compensation and other accrued liabilities

5,599

850

Operating lease liability and right-of-use asset

Deferred revenue

15,000

(6)

Deferred rent

182

Net cash flows used in operating activities

(43,613)

(28,553)

Investing Activities

Proceeds from maturities of short-term investments

157,433

127,967

Purchase of short-term investments

(129,977)

(198,912)

Purchases of property and equipment

(64)

(376)

Net cash flows provided by (used in) investing activities

27,392

(71,321)

Financing Activities

Payments for the redemption of redeemable convertible notes

(5,082)

Issuance of common stock for secondary public offering, net of issuance costs

106,762

Issuance of common stock from stock grants and option exercises

327

107

Proceeds from exercise of warrants

9,545

Net cash flows provided by financing activities

327

111,332

Net (decrease) increase in cash, cash equivalents and restricted cash

(15,894)

11,458

Cash, cash equivalents and restricted cash at beginning of the period

31,263

^[1]

19,805

Cash, cash equivalents and restricted cash at end of the period

^[1]

15,369

31,263

Supplemental Disclosure of Non-Cash Investing and Financing Activities:

Adoption of ASC 606

207

Conversion of redeemable convertible notes to common stock

$ 3

Right-of-use asset and operating lease liability recorded upon the adoption of ASC 842

$ 2,052

[1]	(a) The following table provides a reconciliation of cash and restricted cash to amounts reported within the consolidated balance sheets:

Assets and Liabilities Measured at Fair Value (Detail) - USD ($)
$ in Thousands

Dec. 31, 2019

Dec. 31, 2018

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

$ 76,865

$ 119,053

Money Market Funds

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[1]

15,369

29,090

Restricted cash

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[2]

U.S. Government Agency Securities

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

51,490

^[3]

74,139

^[4]

Federal Agency Securities

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[1]

999

Federal Agency Securities | Short-Term Investments

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[3]

10,006

14,775

Fair Value, Inputs, Level 1

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

66,859

103,279

Fair Value, Inputs, Level 1 | Money Market Funds

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[1]

15,369

29,090

Fair Value, Inputs, Level 1 | Restricted cash

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[2]

Fair Value, Inputs, Level 1 | U.S. Government Agency Securities

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

51,490

^[3]

74,139

^[4]

Fair Value, Inputs, Level 2

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

10,006

15,774

Fair Value, Inputs, Level 2 | Federal Agency Securities

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[1]

999

Fair Value, Inputs, Level 2 | Federal Agency Securities | Short-Term Investments

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets, fair value

^[3]

$ 10,006

$ 14,775

[1]	Included in cash and cash equivalents on accompanying consolidated balance sheet.
[2]	$0.05 million of restricted cash serves as collateral for the Company’s corporate credit card.
[3]	Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.
[4]	Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of the Company and its subsidiary. Intercompany accounts and transactions, if applicable, have been eliminated in consolidation. The Company’s consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles (“GAAP”).
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, convertible notes and related warrants up to the date of conversion, common stock and stock-based compensation. The Company bases its estimates on various assumptions that the Company believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Accounting Pronouncements Recently Adopted	Accounting Pronouncements Recently Adopted Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), to enhance the transparency and comparability of financial reporting related to leasing arrangements. The Company adopted the standard effective January 1, 2019 using the optional transition method and applied the standard only to leases that existed at that date. Under the optional transition method, the Company does not need to restate the comparative periods in transition and will continue to present financial information and disclosures for periods before January 1, 2019 in accordance with ASC Topic 840. The Company also elected relevant optional practical expedients including that the Company did not (1) reassess whether expired or existing contracts are or contain a lease, (2) reassess the lease classifications or reassess the initial direct costs associated with expired or existing leases, and (3) separate lease and non-lease components of its operating leases in which it is the lessee. The adoption of the new lease accounting standard had an impact of approximately $2.1 million on the Company's assets and liabilities on January 1, 2019 and had no impact on cash provided by or used in operating, investing or financing activities on the Company's consolidated statements of cash flows. The adoption of the new lease accounting standard did not impact previously reported financial results. Financial Instruments In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Topic 825-10), which updates certain aspects of recognition, measurement, presentation and disclosure of financial instruments. Subsequently, in February 2018, the FASB issued ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall (Topic 825-10), which clarifies certain aspects of ASU 2016-01, which includes provisions to accounting for equity investments, financial liabilities under the fair value option and presentation and disclosure requirements for financial instruments. The amended guidance requires equity securities, except for those accounted for under the equity method of accounting, with determinable fair values to be measured at fair value with changes in fair value recognized in net income (loss). The Company adopted ASU 2016-01 and 2018-03 effective January 1, 2018, and this guidance did not have a material impact on the Company’s consolidated financial statements, as the Company only has debt securities in its investment portfolio. Revenue from Contracts with Customers In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASC 606”), which amends the existing accounting standards for revenue recognition. ASU 2014-09 is based on principles that govern the recognition of revenue at an amount an entity expects to be entitled when products are transferred to customers. Subsequently, the FASB has issued the following related standards: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; and ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, (collectively, the “new revenue standards”). The Company adopted ASU No. 2014-09 effective January 1, 2018, using the modified retrospective method through a cumulative adjustment to equity. The Company identified one active collaboration arrangement with multiple deliverables at that time, see Note 12. Under the superseded guidance, deliverables and consideration under the collaboration agreement must be accounted for under a single unit of accounting along with other arrangement deliverables and consideration that does not have stand-alone value and are recognized as revenue over the estimated period that the performance obligations are to be performed. Under ASU No. 2014-09, however, the total arrangement consideration is allocated to each performance obligation based on its estimated stand-alone selling price and revenue is recognized as each performance obligation is satisfied. As a result, revenue from the collaboration arrangement of $0.2 million was adjusted to record in an early accounting period upon the adoption of ASU No. 2014-09 as an increase to the Company’s opening balance of accumulated deficit. Classification of certain cash receipts and cash payments in the statement of cash flows In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The standard provides guidance on how certain cash receipts and payments are presented and classified in the statement of cash flows. The standard is intended to reduce current diversity in practice. The Company adopted ASU 2016-15 effective January 1, 2018, and this guidance did not have an impact on the Company’s financial statements. New Accounting Pronouncements – Issued But Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments, or ASU 2016-13. The main objective of ASU 2016-13 is to provide financial statement users with more decision-useful information about an entity's expected credit losses on financial instruments and other commitments to extend credit at each reporting date. To achieve this objective, the amendments in this update replace the incurred loss impairment methodology currently used today with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to develop credit loss estimates. Subsequent to issuing ASU 2016-13, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments – Credit Losses, for the purpose of clarifying certain aspects of ASU 2016-13. In May 2019, the FASB issued ASU 2019-05, Financial Instruments – Credit Losses (Topic 326): Targeted Transition Relief, to provide entities with more flexibility in applying the fair value option on adoption of the credit impairment standard. ASU 2018-19 and ASU 2019-05 have the same effective date and transition requirements as ASU 2016-13. ASU 2016-13 will be effective for all entities except public companies that are not smaller reporting companies for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years, using a modified retrospective approach. Early adoption is permitted. The Company plans to adopt ASU 2016-13 and related updates as of January 1, 2023. The Company will assess the impact of adoption of this standard on its consolidated financial statements. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808) (“ASC 808”): Clarifying the Interaction Between Topic 808 and Topic 606. The amended guidance precludes presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. The new guidance is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted. The Company plans to adopt ASU 2018-18 as of January 1, 2020. The Company does not expect the adoption of ASU 2018-18 to have a material impact on its consolidated financial statements.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company invests its excess cash in bank deposits, consisting primarily of money market mutual funds. The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy requires that an entity maximize the use of observable inputs when estimating fair value. The fair value hierarchy includes the following three-level classification which is based on the market observability of the inputs used for estimating the fair value of the assets or liabilities being measured: Level 1 – Quoted prices in active markets for identical assets or liabilities. Level 2 – Observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 – Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, which are three years for computer equipment and software, and three to seven years for furniture and leasehold improvements.
Investments	Investments The Company invests its excess cash in investment grade, short to intermediate-term, fixed income securities and recognizes purchased securities on the settlement date. All investments have been classified as “available-for-sale” and are carried at estimated fair value based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments at the time of purchase and reevaluates such designation as of each balance sheet date. Unrealized gains and losses on available-for-sale debt securities are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value determined to be other-than-temporary, if any, on available-for-sale debt securities are included in interest and other income, net. The cost of securities sold is based on the specific-identification method. Interest on short-term investments is included in interest and other income, net.
Revenue Recognition	Revenue Recognition License and Collaboration Arrangements Effective January 1, 2018, the Company adopted Accounting Standards Codification (“ASC”) 606 using the modified retrospective method and applied the standard only to contracts that were still active or in place at that date. The Company may enter into collaboration arrangements that fall under the scope Collaborative Arrangements (Topic 808). The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808 to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. The accounting for some of the activities under collaboration arrangements may be analogized to ASC 606 for distinct units of account that are reflective of a vendor-customer relationship. Under ASC 606, in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when the Company satisfies each performance obligation. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues attributed to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgement 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. At the inception of each arrangement that contain development milestones, the Company evaluates whether the development milestones included are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not generally considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of any development milestones, and if necessary, adjusts its estimate of the transaction price. Any such adjustments would be recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. For research and development services, the Company elected the practical expedient to recognize revenue as the research and development services are invoiced. The transaction price is allocated to each performance obligation on a relative stand-alone selling price (“SSP”) basis. The Company recognizes revenue as or when the performance obligations under the contract are satisfied. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the timing of recognition and the SSP for each performance obligation identified in the contract. The SSP for licenses are calculated using the residual approach if the Company has not yet established a price for such license and the license has not previously been sold on a standalone basis. Otherwise, selling prices for licenses are determined using an income approach model and include key assumptions such as: development timeline, revenue forecast, commercialization expenses, discount rate and probabilities of technical and regulatory success. To estimate the SSP for research and development services, the Company uses a cost-plus margin approach. As of December 31, 2019, the Company recorded $15.0 million of deferred revenue from a license and collaboration agreement that was executed on December 18, 2019. See Note 12.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Research and development costs consist of payroll and other personnel-related expenses, laboratory supplies and reagents, contract research and development services, and consulting costs, as well as allocations of facilities and other overhead costs. Under the Company’s collaboration agreements, certain specific expenditures are reimbursed by third parties. During the years ended December 31, 2019 and 2018, the Company recorded a reduction to research and development expenses of $0.0 million and $0.05 million, respectively related to these reimbursements.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents, investments and restricted cash. The Company’s investment policy restricts cash investments to high credit quality, investment grade investments. The Company believes that it has established guidelines for investment of its excess cash that maintain safety and liquidity through its policies on high quality of investment and investment duration. The Company is exposed to credit risk in the event of default by the institutions holding the cash and cash equivalents to the extent of the amounts recorded on the balance sheets. The Company’s accounts receivable as of December 31, 2019 of $15.0 million was due from one party, see Note 12. The amount was subsequently received in full.
Contract Balances	Contract Balances Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. Customer payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under the arrangements. The Company regularly reviews the outstanding accounts receivable, including consideration of factors such as the age of the receivable balance. As of December 31, there was no allowance for doubtful accounts deemed necessary.
Income Taxes	Income Taxes Income taxes are computed using the liability method. Deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company follows the authoritative guidance on accounting for uncertainty in income taxes. This guidance prescribes a more-likely-than-not threshold for financial statement recognition and measurement of a tax position taken in the Company’s income tax returns. This interpretation also provides guidance on accounting for interest and penalties and associated with tax positions, accounting for income taxes in interim periods and income tax disclosures. The Company’s policy is to include penalties and interest expense related to income taxes as a component of other expense and interest expense, respectively, as necessary.
Stock-Based Compensation	Stock-Based Compensation The Company measures the cost of employee, non-employee and director services received in exchange for an award of equity instruments based on the fair value of the award on the date of grant and recognizes the related expense over the period during which the employee, non-employee or director is required to provide service in exchange for the award on a straight-line basis. The Company uses the Black-Scholes option-pricing valuation model to estimate the grant-date fair value of stock-based awards. The determination of fair value for stock-based awards on the date of grant using an option-pricing model requires management to make certain assumptions regarding a number of variables. Upon adoption of ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, the Company elected to account for forfeitures when they occur. As such, the Company recognizes stock-based compensation expense, over their requisite service period, based on the vesting provisions of the individual grants.
Leases	Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. The Company has elected to combine lease and non-lease components as a single component. The lease expense is recognized over the expected term on a straight-line basis. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities, current and operating lease liabilities, non-current.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss of the Company for all periods presented.
Reclassification	Reclassification Certain amounts for the year ended December 31, 2018 have been reclassified, to be consistent with the current year's presentation.

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Summary of Warrant Activity

The following is a summary of warrant activity for the year ended December 31, 2019 and 2018:

	Number of Shares			Weighted Average
	Underlying Warrants			Exercise Price
Outstanding — December 31, 2017		1,751,708		$	6.46
Issued		—
Exercised		(1,735,419	)	$	5.50
Forfeited/Cancelled⁽¹⁾		(6,095	)	$	5.50
Outstanding — December 31, 2018		10,194		$	155.73
Issued		—
Exercised		—
Forfeited/Cancelled		(2,337	)	$	499.50
Outstanding — December 31, 2019		7,857		$	53.61

(1)	In November 2018, 1,845 warrants were cancelled by Healthcare Ventures VIII, a related party.

Leases

12 Months Ended

Dec. 31, 2019

Lessee Disclosure [Abstract]

Leases

The Company leases office space for its corporate headquarters, located in South San Francisco, CA. The lease term is through April 30, 2023 and there are no stated renewal options. Operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term. In calculating the present value of the lease payments, the Company has elected to utilize its incremental borrowing rate based on the original lease term and not the remaining lease term. The lease includes non-lease components (e.g., common area maintenance) that are paid separately from rent based on actual costs incurred and therefore were not included in the right-of-use asset and lease liability but are reflected as an expense in the period incurred.

For the year ended December 31, 2019, the Company’s operating lease expense was $0.6 million. The present value assumptions used in calculating the present value of the lease payments were as follows:

Weighted-average remaining lease term				3.33 years
Weighted-average discount rate					6.0	%

The maturity of the Company’s operating lease liabilities as of December 31, 2019 were as follows (in thousands):

Undiscounted lease payments	Operating Leases
2020	$	578
2021		596
2022		613
2023		209
Total undiscounted lease payments	$	1,996
Less: imputed interest		(194	)
Total operating lease liability		1,802
Less: current portion of operating lease liability		483
Operating lease liability, noncurrent	$	1,319

Supplemental cash flow information for the year ended December 31, 2019 related to operating leases was as follows (in thousands):

Cash paid for leases that were included in operating cash

outflows

562

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following tables present the fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of December 31, 2019 and 2018 (in thousands):

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	15,369	$	—	$	—	$	15,369
U.S. government agency securities⁽²⁾		51,490		—		—		51,490
Federal agency securities⁽²⁾		—		10,006		—		10,006
Total financial assets	$	66,859	$	10,006	$	—	$	76,865

(1)	Included in cash and cash equivalents on accompanying consolidated balance sheet.

(2)	Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.

	December 31, 2018
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	29,090	$	—	$	—	$	29,090
Federal agency securities⁽¹⁾		—		999		—		999
Restricted cash ⁽²⁾		50		—		—		50
U.S. government agency securities⁽³⁾		74,139		—		—		74,139
Federal agency securities⁽³⁾		—		14,775		—		14,775
Total financial assets	$	103,279	$	15,774	$	—	$	119,053

(1)	Included in cash and cash equivalents on accompanying consolidated balance sheet.

(2)	$0.05 million of restricted cash serves as collateral for the Company’s corporate credit card.

(3)	Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.

Related Parties

12 Months Ended

Dec. 31, 2019

Related Parties

8.	Related Parties

On October 24, 2017, the Company announced a strategic research collaboration with Mosaic Biosciences, Inc. (“Mosaic”) to develop intravitreal anti-complement factor 3 (C3) products for the treatment of dry Age-related Macular Degeneration (AMD) and other retinal diseases. Dr. Usman, the Company’s Chief Executive Officer and a member of the Company’s board of directors, and Mr. Lawlor, a member of the Company’s board of directors, are also members of the board of directors of Mosaic. On December 21, 2018, the Company amended its collaboration agreement with Mosaic to, among other things, include certain additional products. According to the Mosaic collaboration agreement, as amended, the Company and Mosaic co-funded certain research. Expenses related to the co-funded research were $1.1 million and $1.3 million for the years ended December 31, 2019 and 2018, respectively.

On December 18, 2019, the Company entered into the second amendment to the Mosaic collaboration agreement, which added future fees for services upon completion of the co-funded research. Also, Mosaic will perform all future services for a fee. Mosaic is entitled to a low double-digit percentage of funds the Company receives from any C3 collaboration. Mosaic is also entitled to sublicense fees and/or research and development and commercial milestones and royalties on one non-C3 complement product. In connection with the Biogen collaboration, the Company received a $15.0 million upfront license fee on January 10, 2020, see Note 12, and Mosaic is entitled to a $3 million payment from the Company.

Stockholders' Equity

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Stockholders' Equity

14.	Stockholders’ Equity

In connection with the closing of an underwritten public offering on April 12, 2017, the Company issued Series A Preferred Stock. During the year ended December 31, 2018, 3,680 shares of the Series A Preferred Stock were converted into 736,000 shares of common stock of the Company. As of December 31, 2018, there were no shares of Series A Preferred stock issued and outstanding.

On February 13, 2018, the Company entered into an underwriting agreement with JonesTrading, in connection with a registered firm commitment underwritten public offering of 2,941,176 shares of common stock, pursuant to a shelf registration statement that was declared effective by the SEC on February 6, 2018. On February 15, 2018 the Company sold 3,382,352 shares of common stock (including 441,176 shares of common stock sold pursuant to the exercise of the underwriters’ overallotment option) at a price to the public of $34.00 per share. The net proceeds to the Company, after deducting the underwriting discounts and commissions and offering expenses payable by the Company were approximately $106.8 million.

In connection with the closing of the underwritten public offering on April 12, 2017, the Company also issued warrants to purchase 2,070,000 shares of common stock at an exercise price of $5.50 per share. Upon their issuance, the common stock warrants were determined to be equity instruments under ASC 480 and ASC 815-40. The net proceeds allocated to the warrants based on a relative fair value basis resulted in $5.0 million being allocated to the warrants. As of December 31, 2019, the Company had no warrants outstanding associated with this offering.

The following is a summary of warrant activity for the year ended December 31, 2019 and 2018:

	Number of Shares			Weighted Average
	Underlying Warrants			Exercise Price
Outstanding — December 31, 2017		1,751,708		$	6.46
Issued		—
Exercised		(1,735,419	)	$	5.50
Forfeited/Cancelled⁽¹⁾		(6,095	)	$	5.50
Outstanding — December 31, 2018		10,194		$	155.73
Issued		—
Exercised		—
Forfeited/Cancelled		(2,337	)	$	499.50
Outstanding — December 31, 2019		7,857		$	53.61

(1)	In November 2018, 1,845 warrants were cancelled by Healthcare Ventures VIII, a related party.

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Contract revenue		$ 6
Type of Revenue [Extensible List]	cbio:ContractMember	cbio:ContractMember
Operating expenses:
Research and development	$ 43,859	$ 21,474
General and administrative	13,418	12,354
Total operating expenses	57,277	33,828
Loss from operations	(57,277)	(33,822)
Interest and other income, net	2,099	3,767
Net loss	$ (55,178)	$ (30,055)
Net loss per share attributable to common stockholders, basic and diluted	$ (4.60)	$ (2.68)
Shares used to compute net loss per share attributable to common stockholders, basic and diluted	12,004,489	11,213,884

Unrecognized tax benefit (Detail) - USD ($) $ in Thousands	12 Months Ended
Unrecognized tax benefit (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Beginning Balance	$ 1,573	$ 1,475
Increase/(Decrease) of unrecognized tax benefits taken in prior years	45	13
Increase/(Decrease) of unrecognized tax benefits related to current year	253	85
Ending Balance	$ 1,871	$ 1,573

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

11.	Income Taxes

The Company has incurred cumulative net operating losses since inception and, consequently, has not recorded any income tax expense for the years ended December 31, 2019 and 2018 due to its net operating loss position.

The reconciliation of the federal statutory income tax rate to the Company’s effective tax rate for the years ended December 31, 2019 and 2018 are as follows:

	Year Ended December 31,
	2019			2018
Tax at statutory federal rate		-21.00	%		-21.00	%
State Tax (benefit)—net of federal benefit		-0.06	%		-0.03	%
Permanent differences		0.43	%		0.68	%
Tax credits		-11.20	%		-0.76	%
Derecognition due to Sec. 382 and 383 limitations		0.00	%		-20.16	%
Change in valuation allowance		31.20	%		39.33	%
Other		0.63	%		1.94	%
Effective tax rate		0.00	%		0.00	%

Significant components of the Company’s deferred tax assets as of December 31, 2019 and 2018 consist of the following (in thousands):

	Year Ended December 31,
	2019			2018
Deferred tax assets:
Accruals and reserves	$	936		$	751
Net operating loss carry forwards		34,392			23,559
Tax credit carry forwards		9,945			3,772
Fixed and intangible assets		10			3
Valuation allowance		(45,283	)		(28,085	)
Net deferred tax assets:	$	—		$	—

Based on the available objective evidence at December 31, 2019, the Company does not believe it is more likely than not that the net deferred tax assets will be realizable. Accordingly, the Company has provided a full valuation allowance against its net deferred tax assets at December 31, 2019 and 2018.

As of December 31, 2019, after consideration of certain limitations (see below), the Company had approximately $163.8 million federal and $64.6 million state net operating loss carryforwards (“NOL”) available to reduce future taxable income which, if unused, will begin to expire in 2032 for federal and 2028 for state tax purposes. The federal net operating loss carryforward includes $80.1 million that have an indefinite life.

As of December 31, 2019, the Company also had tax credit carry forwards available to offset future tax liabilities of approximately $6.2 million for federal and $4.7 million for state. If unused, the federal credit will begin to expire in 2037 and the state tax credit does not expire.

If the Company experiences a greater than 50 percent aggregate change in ownership over a three-year period (a Section 382 ownership change), utilization of its pre-change NOL carryforwards are subject to annual limitation under Section 382 of the Internal Revenue Code (California has similar provisions). The annual limitation is determined by multiplying the value of the Company's stock at the time of such ownership change by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the NOL carryforwards before utilization. The Company determined that ownership changes occurred December 31, 2007, August 20, 2015, April 13, 2017, and February 15, 2018. Approximately $80.1 million and $14.2 million of the NOLs will expire unutilized for federal and California purposes, respectively. The Company has derecognized NOL related deferred tax assets in the tax affected amounts of $16.8 million and $0.0 million for federal and California purposes, respectively.

All of the federal R&D credits could expire unutilized, whereas none of the California R&D credits are subject to expiration. Approximately $6.1 million of gross federal R&D credit-related deferred tax assets were derecognized due to the Section 383 limitation. The ability of the Company to use its remaining NOL carryforwards may be further limited if the Company experiences a Section 382 ownership change as a result of future changes in its stock ownership.

Accounting for Uncertainty in Income Taxes

The Company only recognizes tax benefits if it is more likely than not that they will be sustained upon audit by the relevant tax authority based upon their technical merits. An uncertain tax position will not be recognized if it has less than a 50% likelihood of being sustained.

The Company had approximately $1.9 million and $1.6 million of unrecognized tax benefits as of December 31, 2019 and 2018, respectively. As the Company has a full valuation allowance on its deferred tax assets, the unrecognized tax benefits have reduced the deferred tax assets and the valuation allowance in the same amount. The Company does not expect the amount of unrecognized tax benefits to materially change in the next twelve months.

A reconciliation of the beginning and ending balance of the unrecognized tax benefits is as follows (in thousands):

Beginning Balance at January 1, 2018	$	1,475
Increase/(Decrease) of unrecognized tax benefits taken in prior years		13
Increase/(Decrease) of unrecognized tax benefits related to current year		85
Ending Balance at December 31, 2018	$	1,573
Increase/(Decrease) of unrecognized tax benefits taken in prior years		45
Increase/(Decrease) of unrecognized tax benefits related to current year		253
Ending Balance at December 31, 2019	$	1,871

Interest and penalties related to unrecognized tax benefits would be included as income tax expense in the Company’s consolidated statements of operations. As of December 31, 2019 and 2018, the Company had not recognized any tax-related penalties or interest in its consolidated financial statements.

The Company files income tax returns in the United States federal, California, and New Jersey state jurisdictions. The Company is not currently under examination by income tax authorities in federal, state or other jurisdictions. As of December 31, 2019 and 2018, the Company had no uncertain tax positions which affected its financial position as its results of operations or its cash flow, and will continue to evaluate for uncertain tax positions in the future. The Company is subject to United States federal and state income tax examinations by authorities for all tax years due to accumulated net operating losses that are being carried forward for tax purposes.

Detail of Interest and Other Income, Net (Detail) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Other Income And Expenses [Abstract]

Interest income

$ 2,145

$ 2,229

Dividend income

Miscellaneous (expense) income

^[1]

(39)

1,650

Loss on disposal of property and equipment

(116)

Other

(7)

Total interest and other income, net

$ 2,099

$ 3,767

[1]	$1.7 million miscellaneous income for the year ended December 31, 2018 is mainly composed of a $1.5 million milestone payment received under an agreement associated with neuronal nicotinic receptor (“NNR”) assets sold in 2016.

Other Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Schedule of Other Accrued Liabilities

Other accrued liabilities consisted of the following (in thousands):

	Year Ended December 31,
	2019		2018
Manufacturing	$	4,320	$	1,012
Professional and consulting services		2,026		597
Clinical		435		234
Other		250		200
Total other accrued liabilities	$	7,031	$	2,043

Nature of Operations

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Operations

1.	Nature of Operations

Catalyst Biosciences, Inc. and its subsidiary (the “Company” or “Catalyst”) is a clinical-stage biopharmaceutical company focused on developing novel treatments for hemophilia and other rare bleeding disorders using its engineered subcutaneous (SQ) coagulation factors that promote blood clotting. The Company is located in South San Francisco, California and operates in one segment.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

3.	Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements include the accounts of the Company and its subsidiary. Intercompany accounts and transactions, if applicable, have been eliminated in consolidation. The Company’s consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles (“GAAP”).

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, convertible notes and related warrants up to the date of conversion, common stock and stock-based compensation. The Company bases its estimates on various assumptions that the Company believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Accounting Pronouncements Recently Adopted

Leases

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), to enhance the transparency and comparability of financial reporting related to leasing arrangements. The Company adopted the standard effective January 1, 2019 using the optional transition method and applied the standard only to leases that existed at that date. Under the optional transition method, the Company does not need to restate the comparative periods in transition and will continue to present financial information and disclosures for periods before January 1, 2019 in accordance with ASC Topic 840. The Company also elected relevant optional practical expedients including that the Company did not (1) reassess whether expired or existing contracts are or contain a lease, (2) reassess the lease classifications or reassess the initial direct costs associated with expired or existing leases, and (3) separate lease and non-lease components of its operating leases in which it is the lessee. The adoption of the new lease accounting standard had an impact of approximately $2.1 million on the Company's assets and liabilities on January 1, 2019 and had no impact on cash provided by or used in operating, investing or financing activities on the Company's consolidated statements of cash flows. The adoption of the new lease accounting standard did not impact previously reported financial results.

Financial Instruments

In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Topic 825-10), which updates certain aspects of recognition, measurement, presentation and disclosure of financial instruments. Subsequently, in February 2018, the FASB issued ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall (Topic 825-10), which clarifies certain aspects of ASU 2016-01, which includes provisions to accounting for equity investments, financial liabilities under the fair value option and presentation and disclosure requirements for financial instruments. The amended guidance requires equity securities, except for those accounted for under the equity method of accounting, with determinable fair values to be measured at fair value with changes in fair value recognized in net income (loss). The Company adopted ASU 2016-01 and 2018-03 effective January 1, 2018, and this guidance did not have a material impact on the Company’s consolidated financial statements, as the Company only has debt securities in its investment portfolio.

Revenue from Contracts with Customers

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASC 606”), which amends the existing accounting standards for revenue recognition. ASU 2014-09 is based on principles that govern the recognition of revenue at an amount an entity expects to be entitled when products are transferred to customers. Subsequently, the FASB has issued the following related standards: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; and ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, (collectively, the “new revenue standards”). The Company adopted ASU No. 2014-09 effective January 1, 2018, using the modified retrospective method through a cumulative adjustment to equity. The Company identified one active collaboration arrangement with multiple deliverables at that time, see Note 12. Under the superseded guidance, deliverables and consideration under the collaboration agreement must be accounted for under a single unit of accounting along with other arrangement deliverables and consideration that does not have stand-alone value and are recognized as revenue over the estimated period that the performance obligations are to be performed. Under ASU No. 2014-09, however, the total arrangement consideration is allocated to each performance obligation based on its estimated stand-alone selling price and revenue is recognized as each performance obligation is satisfied. As a result, revenue from the collaboration arrangement of $0.2 million was adjusted to record in an early accounting period upon the adoption of ASU No. 2014-09 as an increase to the Company’s opening balance of accumulated deficit.

Classification of certain cash receipts and cash payments in the statement of cash flows

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The standard provides guidance on how certain cash receipts and payments are presented and classified in the statement of cash flows. The standard is intended to reduce current diversity in practice. The Company adopted ASU 2016-15 effective January 1, 2018, and this guidance did not have an impact on the Company’s financial statements.

New Accounting Pronouncements – Issued But Not Yet Adopted

In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments, or ASU 2016-13. The main objective of ASU 2016-13 is to provide financial statement users with more decision-useful information about an entity's expected credit losses on financial instruments and other commitments to extend credit at each reporting date. To achieve this objective, the amendments in this update replace the incurred loss impairment methodology currently used today with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to develop credit loss estimates. Subsequent to issuing ASU 2016-13, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments – Credit Losses, for the purpose of clarifying certain aspects of ASU 2016-13. In May 2019, the FASB issued ASU 2019-05, Financial Instruments – Credit Losses (Topic 326): Targeted Transition Relief, to provide entities with more flexibility in applying the fair value option on adoption of the credit impairment standard. ASU 2018-19 and ASU 2019-05 have the same effective date and transition requirements as ASU 2016-13. ASU 2016-13 will be effective for all entities except public companies that are not smaller reporting companies for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years, using a modified retrospective approach. Early adoption is permitted. The Company plans to adopt ASU 2016-13 and related updates as of January 1, 2023. The Company will assess the impact of adoption of this standard on its consolidated financial statements.

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808) (“ASC 808”): Clarifying the Interaction Between Topic 808 and Topic 606. The amended guidance precludes presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. The new guidance is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted. The Company plans to adopt ASU 2018-18 as of January 1, 2020. The Company does not expect the adoption of ASU 2018-18 to have a material impact on its consolidated financial statements.

Cash and Cash Equivalents

The Company invests its excess cash in bank deposits, consisting primarily of money market mutual funds. The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents.

Fair Value of Financial Instruments

The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.

The fair value hierarchy requires that an entity maximize the use of observable inputs when estimating fair value. The fair value hierarchy includes the following three-level classification which is based on the market observability of the inputs used for estimating the fair value of the assets or liabilities being measured:

Level 1 – Quoted prices in active markets for identical assets or liabilities.

Level 2 – Observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 – Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, which are three years for computer equipment and software, and three to seven years for furniture and leasehold improvements.

Investments

The Company invests its excess cash in investment grade, short to intermediate-term, fixed income securities and recognizes purchased securities on the settlement date. All investments have been classified as “available-for-sale” and are carried at estimated fair value based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments at the time of purchase and reevaluates such designation as of each balance sheet date. Unrealized gains and losses on available-for-sale debt securities are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value determined to be other-than-temporary, if any, on available-for-sale debt securities are included in interest and other income, net. The cost of securities sold is based on the specific-identification method. Interest on short-term investments is included in interest and other income, net.

Revenue Recognition

License and Collaboration Arrangements

Effective January 1, 2018, the Company adopted Accounting Standards Codification (“ASC”) 606 using the modified retrospective method and applied the standard only to contracts that were still active or in place at that date.

The Company may enter into collaboration arrangements that fall under the scope Collaborative Arrangements (Topic 808). The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808 to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. The accounting for some of the activities under collaboration arrangements may be analogized to ASC 606 for distinct units of account that are reflective of a vendor-customer relationship.

Under ASC 606, in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when the Company satisfies each performance obligation.

If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues attributed to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgement 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.

At the inception of each arrangement that contain development milestones, the Company evaluates whether the development milestones included are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not generally considered probable of being achieved until those approvals are received.

At the end of each reporting period, the Company re-evaluates the probability of achievement of any development milestones, and if necessary, adjusts its estimate of the transaction price. Any such adjustments would be recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. For research and development services, the Company elected the practical expedient to recognize revenue as the research and development services are invoiced.

The transaction price is allocated to each performance obligation on a relative stand-alone selling price (“SSP”) basis. The Company recognizes revenue as or when the performance obligations under the contract are satisfied. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the timing of recognition and the SSP for each performance obligation identified in the contract.

The SSP for licenses are calculated using the residual approach if the Company has not yet established a price for such license and the license has not previously been sold on a standalone basis. Otherwise, selling prices for licenses are determined using an income approach model and include key assumptions such as: development timeline, revenue forecast, commercialization expenses, discount rate and probabilities of technical and regulatory success. To estimate the SSP for research and development services, the Company uses a cost-plus margin approach. As of December 31, 2019, the Company recorded $15.0 million of deferred revenue from a license and collaboration agreement that was executed on December 18, 2019. See Note 12.

Research and Development Expenses

Research and development costs are expensed as incurred. Research and development costs consist of payroll and other personnel-related expenses, laboratory supplies and reagents, contract research and development services, and consulting costs, as well as allocations of facilities and other overhead costs. Under the Company’s collaboration agreements, certain specific expenditures are reimbursed by third parties. During the years ended December 31, 2019 and 2018, the Company recorded a reduction to research and development expenses of $0.0 million and $0.05 million, respectively related to these reimbursements.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents, investments and restricted cash. The Company’s investment policy restricts cash investments to high credit quality, investment grade investments. The Company believes that it has established guidelines for investment of its excess cash that maintain safety and liquidity through its policies on high quality of investment and investment duration. The Company is exposed to credit risk in the event of default by the institutions holding the cash and cash equivalents to the extent of the amounts recorded on the balance sheets. The Company’s accounts receivable as of December 31, 2019 of $15.0 million was due from one party, see Note 12. The amount was subsequently received in full.

Contract Balances

Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. Customer payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under the arrangements. The Company regularly reviews the outstanding accounts receivable, including consideration of factors such as the age of the receivable balance. As of December 31, there was no allowance for doubtful accounts deemed necessary.

Income Taxes

Income taxes are computed using the liability method. Deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse.

The Company follows the authoritative guidance on accounting for uncertainty in income taxes. This guidance prescribes a more-likely-than-not threshold for financial statement recognition and measurement of a tax position taken in the Company’s income tax returns. This interpretation also provides guidance on accounting for interest and penalties and associated with tax positions, accounting for income taxes in interim periods and income tax disclosures.

The Company’s policy is to include penalties and interest expense related to income taxes as a component of other expense and interest expense, respectively, as necessary.

Stock-Based Compensation

The Company measures the cost of employee, non-employee and director services received in exchange for an award of equity instruments based on the fair value of the award on the date of grant and recognizes the related expense over the period during which the employee, non-employee or director is required to provide service in exchange for the award on a straight-line basis.

The Company uses the Black-Scholes option-pricing valuation model to estimate the grant-date fair value of stock-based awards. The determination of fair value for stock-based awards on the date of grant using an option-pricing model requires management to make certain assumptions regarding a number of variables. Upon adoption of ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, the Company elected to account for forfeitures when they occur. As such, the Company recognizes stock-based compensation expense, over their requisite service period, based on the vesting provisions of the individual grants.

Leases

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received.

The Company has elected to combine lease and non-lease components as a single component. The lease expense is recognized over the expected term on a straight-line basis. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities, current and operating lease liabilities, non-current.

Net Loss per Share

Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss of the Company for all periods presented.

Reclassification

Certain amounts for the year ended December 31, 2018 have been reclassified, to be consistent with the current year's presentation.

Collaborations - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Jan. 31, 2020	Dec. 31, 2018	Feb. 28, 2018	Dec. 31, 2019	Dec. 08, 2016
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred revenue				$ 15,000,000
Pfizer Inc \| Collaboration Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment			$ 1,000,000	$ 0
Pfizer Inc \| Collaboration Agreement \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Contingent cash payments upon achievement of clinical, regulatory and commercial milestones					$ 17,500,000
ISU Abxis \| Amended and Restated License Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Regulatory and development milestone payment		$ 2,500,000
ISU Abxis \| Amended and Restated License Agreement \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment		19,500,000
Commercial milestone payments		$ 17,000,000
Biogen \| Exclusive License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research services				30 months
Research services option to extend				12 months
Deferred revenue				$ 15,000,000
Biogen \| Exclusive License \| Subsequent Event
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Up-front payments received	$ 15,000,000
Development milestones payment receivable	340,000,000
Sales milestones receivable.	$ 340,000,000

Leases - Additional Information (Detail) $ in Millions	12 Months Ended
Leases - Additional Information (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Lessee Disclosure [Abstract]
Lease expiration date	Apr. 30, 2023
Lessee operating lease renewal term description	no stated renewal options
Operating lease expense	$ 0.6

Leases (Tables)

12 Months Ended

Dec. 31, 2019

Lessee Disclosure [Abstract]

Summary of Present Value Assumptions used in Calculating Present Value of Lease Payments

The present value assumptions used in calculating the present value of the lease payments were as follows:

Weighted-average remaining lease term				3.33 years
Weighted-average discount rate					6.0	%

Summary of Maturity of Operating Lease Liabilities

The maturity of the Company’s operating lease liabilities as of December 31, 2019 were as follows (in thousands):

Undiscounted lease payments	Operating Leases
2020	$	578
2021		596
2022		613
2023		209
Total undiscounted lease payments	$	1,996
Less: imputed interest		(194	)
Total operating lease liability		1,802
Less: current portion of operating lease liability		483
Operating lease liability, noncurrent	$	1,319

Schedule of Supplemental Cash Flow Information

Supplemental cash flow information for the year ended December 31, 2019 related to operating leases was as follows (in thousands):

Cash paid for leases that were included in operating cash

outflows

562

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2007
Income Tax [Line Items]
Gross federal R&D tax credit-related deferred tax assets derecognized	$ 6,100,000
Unrecognized tax benefit	1,871,000	$ 1,573,000	$ 1,475,000
Tax-related penalties or interest recognized	0	0
Uncertain tax positions	0	$ 0
Federal Income Tax
Income Tax [Line Items]
Net operating loss carryforwards	$ 163,800,000			$ 80,100,000
Net operating loss carryforwards expiration year	2032
Tax credit carryforwards available to offset future federal tax liabilities	$ 6,200,000
Credit carryforward, expire period	Dec. 31, 2037
Net operating loss carryforward,derecognized	$ 16,800,000
State Income Tax
Income Tax [Line Items]
Net operating loss carryforwards	$ 64,600,000
Net operating loss carryforwards expiration year	2028
Tax credit carryforwards available to offset future federal tax liabilities	$ 4,700,000
CALIFORNIA
Income Tax [Line Items]
Net operating loss carryforwards	14,200,000
Net operating loss carryforward,derecognized	$ 0

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Investments All Other Investments [Abstract]

Cash Equivalents, Restricted Cash and Short-Term Investments Classified as Available-for-sale Securities

Cash equivalents, restricted cash and short-term investments, which are classified as available-for-sale securities, consisted of the following (in thousands):

December 31, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	15,369	$	—	$	—	$	15,369
U.S. government agency securities		51,467		23		—		51,490
Federal agency securities		9,995		11		—		10,006
Total financial assets	$	76,831	$	34	$	—	$	76,865
Classified as:
Cash and cash equivalents							$	15,369
Short-term investments								61,496
							$	76,865

December 31, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	29,090	$	—	$	—		$	29,090
Federal agency securities (cash equivalents)		999		—	$	—			999
Restricted cash		50		—		—			50
U.S. government agency securities		74,144		1		(6	)		74,139
Federal agency securities		14,774		1		—			14,775
Total financial assets	$	119,057	$	2	$	(6	)	$	119,053
Classified as:
Cash and cash equivalents								$	30,089
Short-term investments									88,914
Restricted cash									50
								$	119,053

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2017	$ 30,774		$ 6	$ 204,262		$ (173,494)
Balance (in shares) at Dec. 31, 2017		3,680	6,081,230
Opening balance adjustment - adoption of ASC 606 at Dec. 31, 2017	207					207
Balance at Dec. 31, 2017	30,981		$ 6	204,262		(173,287)
Stock-based compensation expense	2,606		6,790	2,606
Issuance of common stock for follow-on offering, net of issuance costs	106,762		$ 4	106,758
Issuance of common stock for follow-on offering, net of issuance costs, shares			3,382,352
Issuance of common stock upon exercise of warrants	9,545		$ 2	9,543
Issuance of common stock upon exercise of warrants, shares			1,735,419
Conversion of preferred stock to common stock, shares		(3,680)	736,000
Issuance of common stock from stock grants and option exercises	107			107
Issuance of common stock from stock grants and option exercises			12,716
Conversion of redeemable convertible notes to common stock	3			3
Conversion of redeemable convertible notes to common stock, shares			21
Unrealized gain (loss) on available-for-sale debt securities	(4)				$ (4)
Net loss	(30,055)					(30,055)
Balance at Dec. 31, 2018	119,945		$ 12	323,279	(4)	(203,342)
Balance (in shares) at Dec. 31, 2018			11,954,528
Stock-based compensation expense	3,204		$ 24,235	3,204
Issuance of common stock from stock grants and option exercises	327			327
Issuance of common stock from stock grants and option exercises			62,072
Unrealized gain (loss) on available-for-sale debt securities	38				38
Net loss	(55,178)					(55,178)
Balance at Dec. 31, 2019	$ 68,336		$ 12	$ 326,810	$ 34	$ (258,520)
Balance (in shares) at Dec. 31, 2019			12,040,835

Cash Equivalents, Restricted Cash and Short-Term Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 76,831	$ 119,057
Gross Unrealized Gains	34	2
Gross Unrealized Losses		(6)
Estimated Fair Value	76,865	119,053
Restricted cash
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		50
Estimated Fair Value		50
Federal Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,995	14,774
Gross Unrealized Gains	11	1
Estimated Fair Value	10,006	14,775
Federal Agency Securities \| Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		999
Estimated Fair Value		999
Money Market Funds \| Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,369	29,090
Estimated Fair Value	15,369	29,090
U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	51,467	74,144
Gross Unrealized Gains	23	1
Gross Unrealized Losses		(6)
Estimated Fair Value	51,490	74,139
Cash and Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	15,369	30,089
Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	$ 61,496	$ 88,914

Interest and Other Income, Net (Tables)

12 Months Ended

Dec. 31, 2019

Other Income And Expenses [Abstract]

Detail of Interest and Other Income, Net

The following table shows the detail of interest and other income, net for the years ended December 31, 2019 and 2018 (in thousands):

	Year Ended December 31,
	2019			2018
Interest income	$	2,145		$	2,229
Dividend income		—			4
Miscellaneous (expense) income⁽¹⁾		(39	)		1,650
Loss on disposal of property and equipment		—			(116	)
Other		(7	)		—
Total interest and other income, net	$	2,099		$	3,767

(1)	$1.7 million miscellaneous income for the year ended December 31, 2018 is mainly composed of a $1.5 million milestone payment received under an agreement associated with neuronal nicotinic receptor (“NNR”) assets sold in 2016.

Schedule of Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Manufacturing	$ 4,320	$ 1,012
Professional and consulting services	2,026	597
Clinical	435	234
Other	250	200
Total other accrued liabilities	$ 7,031	$ 2,043

Summary of Warrant Activity (Parenthetical) (Detail) - shares	1 Months Ended	12 Months Ended
	Nov. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Class Of Warrant Or Right [Line Items]
Number of shares of warrants forfeited/cancelled		2,337	6,095
Healthcare Ventures VIII
Class Of Warrant Or Right [Line Items]
Number of shares of warrants forfeited/cancelled	1,845

Liquidity - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Liquidity [Abstract]
Accumulated deficit	$ 258,520	$ 203,342
Cash, cash equivalents and short-term investments	76,900
Net loss	$ 55,178	$ 30,055

- Definition

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

+ References + Details

Summary of Option Activity Under Company's Equity Incentive Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance	1,361,977	821,741
Number of Shares Underlying Outstanding Options, Options granted	450,900	612,050
Number of Shares Underlying Outstanding Options, Options exercised	(41,219)	(12,716)
Number of Shares Underlying Outstanding Options, Options canceled/forfeited	(182,722)	(43,315)
Number of Shares Underlying Outstanding Options, Options expired	(11,395)	(15,783)
Number of Shares Underlying Outstanding Options, Ending Balance	1,577,541	1,361,977	821,741
Number of Shares Underlying Outstanding Options, Exercisable- December 31, 2019	740,356
Shares available to be granted - December 31, 2019	1,014,126
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance	$ 12.04	$ 13.69
Weighted- Average Exercise Price, Options granted	7.85	13.13
Weighted- Average Exercise Price, Options exercised	4.57	4.17
Weighted- Average Exercise Price, Options Canceled/forfeited	8.36	7.76
Weighted- Average Exercise Price, Options expired	96.49	158.81
Weighted- Average Exercise Price, Ending Balance	10.85	$ 12.04	$ 13.69
Weighted- Average Exercise Price, Exercisable - December 31, 2018	$ 13.30
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	8 years 1 month 24 days	8 years 8 months 15 days	9 years 2 months 1 day
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 2,294	$ 6,376
Aggregate Intrinsic Value, Options exercised	159	213
Aggregate Intrinsic Value, Outstanding	$ 1,350	$ 2,294	$ 6,376

Detail of Interest and Other Income, Net (Parenthetical) (Detail) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Other Income And Expenses [Abstract]

Miscellaneous (expense) income

^[1]

$ (39)

$ 1,650

Milestone payment received

$ 1,500

[1]	$1.7 million miscellaneous income for the year ended December 31, 2018 is mainly composed of a $1.5 million milestone payment received under an agreement associated with neuronal nicotinic receptor (“NNR”) assets sold in 2016.

Liquidity

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Liquidity

The Company had a net loss of $55.2 million for the year ended December 31, 2019 and an accumulated deficit of $258.5 million as of December 31, 2019. The Company expects to continue to incur losses for the next several years. As of December 31, 2019, the Company had $76.9 million of cash, cash equivalents and short-term investments. Its primary uses of cash are to fund operating expenses, including research and development expenditures and general and administrative expenditures. Based on the current status of its research and development plans, the Company believes that its existing cash, cash equivalents and short-term investments as of December 31, 2019 will be sufficient to fund its cash requirements for at least the next 12 months from the date of the filing of this report. If, at any time, the Company’s prospects for financing its research and development programs decline, the Company may decide to reduce research and development expenses by delaying, discontinuing or reducing its funding of one or more of its research or development programs. Alternatively, the Company might raise funds through strategic collaborations, public or private financings or other arrangements. Such funding, if needed, may not be available on favorable terms, or at all.

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Cumulative adjustment to accumulated deficit				$ 207
Deferred revenue from a license and collaboration agreement	$ 15,000
Reduction to research and development expenses	0	$ 50
Accounts receivable	$ 15,000
Software
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Computer equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Furniture \| Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Furniture \| Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	7 years
Leasehold improvements \| Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Leasehold improvements \| Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	7 years
Accumulated Deficit
Summary Of Significant Accounting Policies [Line Items]
Cumulative adjustment to accumulated deficit				$ 207
AS 2016-02
Summary Of Significant Accounting Policies [Line Items]
Lease practical expedients	true
Impact of new lease accounting standard on assets and liabilities	$ 2,100
ASU 2014-09 \| ISU Abxis \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Accumulated Deficit
Summary Of Significant Accounting Policies [Line Items]
Cumulative adjustment to accumulated deficit			$ 200

Summary of Warrant Activity (Detail) - $ / shares	12 Months Ended
Summary of Warrant Activity (Detail) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Warrants And Rights Note Disclosure [Abstract]
Number of Shares Underlying Warrants, Outstanding	10,194	1,751,708
Number of Shares Underlying Warrants, Exercised		(1,735,419)
Number of Shares Underlying Warrants, Forfeited/Cancelled	(2,337)	(6,095)
Number of Shares Underlying Warrants, Outstanding	7,857	10,194
Warrants Outstanding, Weighted Average Exercise Price	$ 155.73	$ 6.46
Warrants Exercised, Weighted Average Exercise Price		5.50
Warrants Forfeited/Cancelled, Weighted Average Exercise Price	499.50	5.50
Warrants Outstanding, Weighted Average Exercise Price	$ 53.61	$ 155.73

Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Option Activity Under Company's Equity Incentive Plans

The following table summarizes stock option activity under the Company’s equity incentive plans and related information:

	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (thousands)
Outstanding — December 31, 2017		821,741		$	13.69		9.17	$	6,376
Options granted		612,050		$	13.13
Options exercised		(12,716	)	$	4.17			$	213
Options canceled/forfeited		(43,315	)	$	7.76
Options expired		(15,783	)	$	158.81
Outstanding — December 31, 2018		1,361,977		$	12.04		8.71	$	2,294
Options granted		450,900		$	7.85
Options exercised		(41,219	)	$	4.57			$	159
Options forfeited		(182,722	)	$	8.36
Options expired		(11,395	)	$	96.49
Outstanding — December 31, 2019		1,577,541		$	10.85		8.15	$	1,350
Exercisable — December 31, 2019		740,356		$	13.30
Shares available to be granted — December 31, 2019		1,014,126

Summary of Weighted Average Valuation Assumptions Used to Estimate Fair Value of Employee Stock Options

The fair value of employee stock options was estimated using the following weighted-average assumptions for the year ended December 31, 2019 and 2018:

	Year Ended December 31,
	2019			2018
Employee Stock Options:
Expected term (in years)		5.98			6.04
Risk-free interest rate		2.35	%		2.67	%
Dividend yield		—			—
Volatility		90.81	%		92.61	%
Weighted-average fair value of stock options granted	$	5.85		$	9.97

Summary of Stock-Based Compensation Recognized

Total stock-based compensation recognized was as follows (in thousands):

	Year Ended December 31,
	2019		2018
Research and development	$	1,052	$	606
General and administrative⁽¹⁾		2,152		2,000
Total stock-based compensation	$	3,204	$	2,606

(1)	Included $0.03 and $0.1 million related to modifications of certain Board member stock options in the years ended December 31, 2019 and 2018, respectively. These modifications extended the post-termination exercise period of certain options.

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

4.	Fair Value Measurements

For a description of the fair value hierarchy and fair value methodology, see “Note 3 – Summary of Significant Accounting Policies”. As of December 31, 2019 and 2018, the Company’s highly liquid money market funds included within cash equivalents, restricted cash and U.S. Treasury securities are valued using Level 1 inputs. The Company classifies its federal agency securities as Level 2. There were no transfers in or out of Level 1 and Level 2 during the periods presented. U.S. Treasury securities are bonds issued by the U.S. government and are fully backed by the U.S. government. Given the frequency at which U.S. Treasury securities trade and the accessibility of observable, quoted prices for such assets in active markets, they are recognized as Level 1 assets. Federal agency securities are bonds and notes issued by government-sponsored enterprises, including Fannie Mae, Freddie Mac and the Federal Home Loan Bank. Since federal agency securities typically do not trade as U.S. Treasury securities and no exchange exists to price such investments, they are recognized as Level 2 assets.

The following tables present the fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of December 31, 2019 and 2018 (in thousands):

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	15,369	$	—	$	—	$	15,369
U.S. government agency securities⁽²⁾		51,490		—		—		51,490
Federal agency securities⁽²⁾		—		10,006		—		10,006
Total financial assets	$	66,859	$	10,006	$	—	$	76,865

(1)	Included in cash and cash equivalents on accompanying consolidated balance sheet.

(2)	Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.

	December 31, 2018
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	29,090	$	—	$	—	$	29,090
Federal agency securities⁽¹⁾		—		999		—		999
Restricted cash ⁽²⁾		50		—		—		50
U.S. government agency securities⁽³⁾		74,139		—		—		74,139
Federal agency securities⁽³⁾		—		14,775		—		14,775
Total financial assets	$	103,279	$	15,774	$	—	$	119,053

(1)	Included in cash and cash equivalents on accompanying consolidated balance sheet.

(2)	$0.05 million of restricted cash serves as collateral for the Company’s corporate credit card.

(3)	Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.

- 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

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Dec. 31, 2019 USD ($)
AGC Biologics, Inc \| Marzeptacog Alfa Activated and Dalcinonacog Alfa
Commitments And Contingencies Disclosure [Line Items]
Clinical trials	$ 12.4
Contractual obligation payments	4.6
Catalent Indiana, LLC. \| Dalcinonacog alfa.
Commitments And Contingencies Disclosure [Line Items]
Clinical trials	0.5
Contractual obligation payments	$ 0.4