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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	May 01, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	CBIO
Entity Registrant Name	Catalyst Biosciences, Inc.
Entity Central Index Key	0001124105
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		17,435,361
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	000-51173
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
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 70,364	$ 15,369
Short-term investments	34,164	61,496
Accounts receivable	1,366	15,000
Prepaid and other current assets	2,381	4,201
Total current assets	108,275	96,066
Other assets, noncurrent	197	257
Right-of-use assets	1,795	1,927
Property and equipment, net	296	304
Total assets	110,563	98,554
Current liabilities:
Accounts payable	1,316	4,279
Accrued compensation	1,268	2,106
Deferred revenue		15,000
Other accrued liabilities	8,774	7,031
Operating lease liability	495	483
Total current liabilities	11,853	28,899
Operating lease liability, noncurrent	1,191	1,319
Total liabilities	13,044	30,218
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; 17,419,313 and 12,040,835 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	17	12
Additional paid-in capital	359,935	326,810
Accumulated other comprehensive income	140	34
Accumulated deficit	(262,573)	(258,520)
Total stockholders’ equity	97,519	68,336
Total liabilities and stockholders’ equity	$ 110,563	$ 98,554

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
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	17,419,313	12,040,835
Common stock, shares outstanding	17,419,313	12,040,835

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
License and collaboration revenue	$ 16,366
Operating expenses:
Total operating expenses	21,434	$ 15,714
Research and development	13,264	12,027
General and administrative	3,691	3,687
Loss from operations	(5,068)	(15,714)
Interest and other income, net	1,015	631
Net loss	$ (4,053)	$ (15,083)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.28)	$ (1.26)
Shares used to compute net loss per share attributable to common stockholders, basic and diluted	14,592,451	11,963,586
License
License and collaboration revenue	$ 15,045
Collaboration
License and collaboration revenue	1,321
Cost of license
Operating expenses:
Total operating expenses	3,047
Cost of collaboration
Operating expenses:
Total operating expenses	$ 1,432

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (4,053)	$ (15,083)
Other comprehensive income:
Unrealized gain on available-for-sale debt securities	106	17
Total comprehensive loss	$ (3,947)	$ (15,066)

- Definition

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

+ References + Details

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
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	829		829
Issuance of common stock from stock grants and option exercises	106		106
Issuance of common stock from stock grants and option exercises, shares		19,576
Unrealized gain on available-for-sale debt securities	17			17
Net loss	(15,083)				(15,083)
Balance at Mar. 31, 2019	105,814	$ 12	324,214	13	(218,425)
Balance (in shares) at Mar. 31, 2019		11,974,104
Balance at Dec. 31, 2019	68,336	$ 12	326,810	34	(258,520)
Balance (in shares) at Dec. 31, 2019		12,040,835
Stock-based compensation expense	805		805
Stock-based compensation expense		7,817
Issuance of common stock from stock grants and option exercises	339		339
Issuance of common stock from stock grants and option exercises, shares		62,969
Issuance of common stock for public offering, net of issuance costs of $2,514	31,986	$ 5	31,981
Issuance of common stock for public offering, net of issuance costs of $2,514, shares		5,307,692
Unrealized gain on available-for-sale debt securities	106			106
Net loss	(4,053)				(4,053)
Balance at Mar. 31, 2020	$ 97,519	$ 17	$ 359,935	$ 140	$ (262,573)
Balance (in shares) at Mar. 31, 2020		17,419,313

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Statement Of Stockholders Equity [Abstract]
Issuance costs of issuance of common stock for public offering	$ 2,514

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

3 Months Ended

Mar. 31, 2020

Mar. 31, 2019

Operating Activities

Net loss

$ (4,053)

$ (15,083)

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

Stock-based compensation expense

805

829

Depreciation and amortization

Changes in operating assets and liabilities:

Accounts receivable

13,634

Prepaid and other current assets

1,880

Accounts payable

(2,963)

(966)

Accrued compensation and other accrued liabilities

866

100

Operating lease liability and right-of-use asset

Deferred revenue

(15,000)

Net cash flows used in operating activities

(4,790)

(14,958)

Investing Activities

Proceeds from maturities of short-term investments

33,457

48,274

Purchase of short-term investments

(6,019)

(39,596)

Purchases of property and equipment

(17)

(15)

Net cash flows provided by investing activities

27,421

8,663

Financing Activities

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

32,025

Issuance of common stock from stock grants and option exercises

339

106

Net cash flow provided by financing activities

32,364

106

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

54,995

(6,189)

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

15,369

31,263

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

^[1]

$ 70,364

25,074

Supplemental Disclosure of Non-Cash Investing and Financing Activities:

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

$ 2,052

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

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

Mar. 31, 2020

Mar. 31, 2019

Statement Of Cash Flows [Abstract]

Cash and cash equivalents

$ 70,364

$ 25,024

Restricted cash

Total cash, cash equivalents and restricted cash

^[1]

$ 70,364

$ 25,074

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

Nature of Operations and Liquidity

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Operations and Liquidity

1.	Nature of Operations and Liquidity

Catalyst Biosciences, Inc. and its subsidiary (the “Company” or “Catalyst”) is a fully integrated research and clinical development biopharmaceutical company with expertise in protease engineering, discovery, translational research, clinical development, and manufacturing. The Company is focused on advancing its protease product candidates in the fields of hemostasis and complement regulation. The Company is located in South San Francisco, California and operates in one segment.

The Company had a net loss of $4.1 million for the three months ended March 31, 2020 and an accumulated deficit of $262.6 million as of March 31, 2020. The Company expects to continue to incur losses for the next several years. As of March 31, 2020, the Company had $104.5 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 March 31, 2020 will be sufficient to fund its cash requirements for at least the next 12 months from the date of the filing of this quarterly 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

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Basis of Presentation

The Company’s condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair presentation of the Company’s financial information. These interim results and cash flows for any interim period are not necessarily indicative of the results to be expected for the full year.

The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the consolidated financial statements filed with the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 (“Annual Report”).

Accounting Pronouncements Recently Adopted

The Company’s significant accounting policies are included in “Part II - Item 8 - Financial Statements and Supplementary Data - Note 3 – Summary of Significant Accounting Policies” in the Company’s Annual Report. In November 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 (“ASU 2018-18”). 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 adopted ASU 2018-18 as of January 1, 2020. The adoption of ASU 2018-18 did not have a material impact on the Company’s condensed consolidated financial statements.

New Accounting Pronouncements Recently Issued But Not Yet Adopted

In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (“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 the Company 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 December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in ASU 2019-12 are intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. ASU 2019-12 is effective for the Company beginning January 1, 2021 with early adoption permitted. The Company is evaluating the impact of adopting this new accounting guidance on its consolidated financial statements.

Cost of License and Collaboration Revenue

Cost of license revenue includes sublicense fees paid or payable to Mosaic Biosciences, Inc. (“Mosaic”), incurred in the period, under the terms of the Mosaic collaboration agreement, and fees for patent development and protection paid or payable to other third-party vendors corresponding to the recognition of license revenue from the Biogen Agreement. See Notes 7 and 11. Cost of license revenue does not include any allocated overhead costs.

Cost of collaboration revenue includes fees for research and development services paid or payable to Mosaic and other third-party vendors and personnel cost, incurred in the period pertaining to the Biogen Agreement. See Notes 7 and 11. Cost of collaboration revenue does not include any allocated overhead costs.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

3.	Fair Value Measurements

For a description of the fair value hierarchy and the Company’s fair value methodology, see “Part II - Item 8 - Financial Statements and Supplementary Data - Note 2 – Summary of Significant Accounting Policies” in the Company’s Annual Report. There were no significant changes in these methodologies during the three months ended March 31, 2020.

There were no transfers in or out of Level 1 or 2 during the periods presented. The following tables present the fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of March 31, 2020 and December 31, 2019 (in thousands):

	March 31, 2020
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	70,364	$	—	$	—	$	70,364
U.S. government agency securities⁽²⁾		28,146		—		—		28,146
Federal agency securities⁽²⁾		—		6,018		—		6,018
Total financial assets	$	98,510	$	6,018	$	—	$	104,528

(1)	Included in cash and cash equivalents on the accompanying condensed consolidated balance sheets.

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

	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 the accompanying condensed consolidated balance sheets.

(2)	Included in short-term investments on the accompanying condensed consolidated balance sheets and 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

Financial Instruments

3 Months Ended

Mar. 31, 2020

Investments All Other Investments [Abstract]

Financial Instruments

4.	Financial Instruments

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

March 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	70,364	$	—	$	—	$	70,364
U.S. government agency securities		28,026		120		—		28,146
Federal agency securities		5,998		20		—		6,018
Total financial assets	$	104,388	$	140	$	—	$	104,528
Classified as:
Cash and cash equivalents							$	70,364
Short-term investments								34,164
							$	104,528

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

There have been no material realized gains or losses on available-for-sale debt securities for the periods presented. As of March 31, 2020, the remaining contractual maturities of available-for-sale debt securities was less than one year.

The carrying amounts of cash, accounts receivable, accounts payable, and accrued liabilities approximate their fair values due to the short-term maturity of these instruments.

Lease

3 Months Ended

Mar. 31, 2020

Lessee Disclosure [Abstract]

Lease

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 three months ended March 31, 2020 and 2019, the Company’s operating lease expense was $0.2 million and $0.2 million, respectively. The present value assumptions used in calculating the present value of the lease payments were as follows:

March 31, 2020

December 31, 2019

Weighted-average remaining lease

term

3.08 years

3.33 years

Weighted-average discount rate

6.0

The maturity of the Company’s operating lease liabilities as of March 31, 2020 were as follows (in thousands):

Remaining in 2020	$	435
2021		596
2022		613
2023		209
Total undiscounted lease payments		1,853
Less imputed interest		(167	)
Total operating lease liability	$	1,686

Supplemental cash flow information related to operating leases was as follows (in thousands):

Three Months Ended March 31,

2020

2019

Cash paid for leases that were

included in operating cash outflows

142

138

Stock Based Compensation

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Based Compensation

6.	Stock Based Compensation

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)
Outstanding — December 31, 2019		1,577,541		$	10.85		8.15
Options granted		469,750		$	6.87
Options exercised		(44,605	)	$	5.04
Options forfeited		(26,116	)	$	16.04
Options expired		(3,918	)	$	67.12
Outstanding — March 31, 2020		1,972,652		$	9.86		8.13
Exercisable — March 31, 2020		808,220		$	12.50

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 5.53 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 three months ended March 31, 2020 and 2019:

	Three Months Ended March 31,
	2020			2019
Employee Stock Options:
Risk-free interest rate		1.57	%		2.56	%
Expected term (in years)		5.53			6.03
Dividend yield		—			—
Volatility		110.00	%		82.91	%
Weighted-average fair value of stock options granted	$	5.58		$	5.80

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

	Three Months Ended March 31,
	2020		2019
Research and development	$	344	$	238
General and administrative⁽¹⁾		461		591
Total stock-based compensation	$	805	$	829

(1)	Included in general and administrative stock-based compensation for the three months ended March 31, 2020 is expense related to 7,817 shares of common stock issued to certain board members in lieu of their cash compensation.

As of March 31, 2020, 276,043 shares of common stock were available for future grant and 1,972,652 options to purchase shares of common stock were outstanding. As of March 31, 2020, the Company had unrecognized employee stock-based compensation expense of $7.1 million, related to unvested stock awards, which is expected to be recognized over an estimated weighted-average period of 2.62 years.

Collaborations

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaborations

7.	Collaborations

Pfizer

Pursuant to the termination agreement entered into on December 8, 2016, in connection with the termination of a prior license and development agreement, Pfizer granted the Company an exclusive license to Pfizer’s proprietary rights for manufacturing materials and processes that apply to Factor VIIa variants, CB 813a and marzeptacog alfa (activated) - MarzAA. Pfizer also transferred to the Company the IND application and documentation related to the development, manufacturing and testing of the Factor VIIa products as well as the orphan drug designation. The Company agreed to make contingent cash payments to Pfizer in an aggregate amount up to $17.5 million, payable upon the achievement of certain clinical, regulatory and commercial milestones. Following commercialization of any covered product, Pfizer will 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 its Phase 2 study; the amount was recorded as a research and development expense. No payments were made to Pfizer in the three months ended March 31, 2020.

ISU Abxis

In December 2018, the Company entered into an amended and restated license agreement with ISU Abxis (the “A&R ISU Abxis Agreement”), which amended and restated its previous license and collaboration agreement with ISU Abxis 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 Abxis 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 Abxis, 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 Abxis, including $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 March 31, 2020, no milestones have 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, with the right to sublicense, license (“Exclusive License”) to develop and commercialize CB 2782-PEG and other anti-C3 proteases for potential treatment of dry age-related macular degeneration (“AMD”) and other 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, or 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 terminated earlier by either party as specified under the agreement.

For the three months ended March 31, 2020, the Company recognized the $15.0 million in license revenue upon the transfer of the Exclusive License and the related know-how, and less than $0.1 million in license revenue for reimbursable out-of-pocket costs incurred.

For the three months ended March 31, 2020, the Company recognized $1.3 million in collaboration revenue for reimbursable out-of-pocket and personnel costs incurred related to research services.

Net Loss per Share Attributable to Common Stockholders

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Net Loss per Share Attributable to Common Stockholders

8.	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 three months ended March 31, 2020 and 2019 (in thousands, except share and per share data):

	Three Months Ended March 31,
	2020			2019
Net loss attributable to common stockholders	$	(4,053	)	$	(15,083	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		14,592,451			11,963,586
Net loss available for common stockholders per share, basic and diluted	$	(0.28	)	$	(1.26	)

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:

	Three Months Ended March 31,
	2020		2019
Options to purchase common stock		1,972,652		1,612,871
Common stock warrants		7,857		10,194
Total		1,980,509		1,623,065

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Stockholders' Equity

9.	Stockholders’ Equity

In February 2020, the Company completed an underwritten public offering of 5,307,692 shares of its common stock (including 692,307 shares sold pursuant to the exercise of the underwriters’ overallotment option) at a price of $6.50 per share. The net proceeds to the Company, after deducting $2.5 million in underwriting discounts and commissions and offering expenses payable by the Company, were approximately $32.0 million.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

10.	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 currently has firm work orders with AGC to manufacture MarzAA and DalcA to support its clinical trials totaling $10.7 million and the payment obligations remaining at March 31, 2020 were $3.4 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 March 31, 2020 were $0.4 million.

The COVID-19 pandemic may disrupt the operations of the Company’s manufacturers or disrupt supply logistics, which could impact the timing of deliveries and potentially increase expenses under our agreements.

Related Parties

3 Months Ended

Mar. 31, 2020

Related Parties

11.	Related Parties

On October 24, 2017, the Company announced a strategic research collaboration with Mosaic to develop intravitreal anti-complement factor C3 products for the treatment of dry 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 collaboration were $0.7 million and $0.3 million for the three months ended March 31, 2020 and 2019, respectively. The amount incurred in 2020 is fully reimbursable under the Biogen Agreement, see Note 7.

In consideration for its co-funded research, 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. On December 18, 2019, the Company entered into the second amendment to the Mosaic collaboration agreement following completion of the co-funded research. Pursuant to the second amendment, any future services provided by Mosaic will be performed on a fee-for-service basis. In connection with the Biogen Agreement, the Company received a $15.0 million upfront license fee on January 10, 2020, see Note 7. The Company paid Mosaic a $3.0 million sublicense fee and recorded such payment as cost of license revenue.

Interest and Other Income, Net

3 Months Ended

Mar. 31, 2020

Other Income And Expenses [Abstract]

Interest and Other Income, Net

12.	Interest and Other Income, Net

The following table shows the detail of interest and other income, net for the three months ended March 31, 2020 and 2019 (in thousands):

	Three Months Ended March 31,
	2020		2019
Interest income	$	334	$	631
Miscellaneous income		679		—
Other		2		—
Total interest and other income, net	$	1,015	$	631

Subsequent Event

3 Months Ended

Mar. 31, 2020

Subsequent Events [Abstract]

Subsequent Event

13.	Subsequent Event

On May 8, 2020, the Company further amended and restated the Mosaic collaboration agreement to provide for a one-time payment of $750,000, plus up to $4.0 million in future milestone payments related to regulatory and clinical development events for CB 2782-PEG and an additional anti-complement product candidate, in lieu of Catalyst’s obligations to pay Mosaic a double-digit percentage of funds the Company receives from Biogen or any other amounts related to sublicense fees, research and development payments, or any other commercial milestones and royalties on any other development candidates. Catalyst will own one hundred percent of all future payment streams related to these product candidates.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair presentation of the Company’s financial information. These interim results and cash flows for any interim period are not necessarily indicative of the results to be expected for the full year. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the consolidated financial statements filed with the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 (“Annual Report”).
Accounting Pronouncements Recently Adopted	Accounting Pronouncements Recently Adopted The Company’s significant accounting policies are included in “Part II - Item 8 - Financial Statements and Supplementary Data - Note 3 – Summary of Significant Accounting Policies” in the Company’s Annual Report. In November 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 (“ASU 2018-18”). 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 adopted ASU 2018-18 as of January 1, 2020. The adoption of ASU 2018-18 did not have a material impact on the Company’s condensed consolidated financial statements. New Accounting Pronouncements Recently Issued But Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (“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 the Company 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 December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in ASU 2019-12 are intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. ASU 2019-12 is effective for the Company beginning January 1, 2021 with early adoption permitted. The Company is evaluating the impact of adopting this new accounting guidance on its consolidated financial statements.
Cost of License and Collaboration Revenue	Cost of License and Collaboration Revenue Cost of license revenue includes sublicense fees paid or payable to Mosaic Biosciences, Inc. (“Mosaic”), incurred in the period, under the terms of the Mosaic collaboration agreement, and fees for patent development and protection paid or payable to other third-party vendors corresponding to the recognition of license revenue from the Biogen Agreement. See Notes 7 and 11. Cost of license revenue does not include any allocated overhead costs. Cost of collaboration revenue includes fees for research and development services paid or payable to Mosaic and other third-party vendors and personnel cost, incurred in the period pertaining to the Biogen Agreement. See Notes 7 and 11. Cost of collaboration revenue does not include any allocated overhead costs.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

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 March 31, 2020 and December 31, 2019 (in thousands):

	March 31, 2020
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	70,364	$	—	$	—	$	70,364
U.S. government agency securities⁽²⁾		28,146		—		—		28,146
Federal agency securities⁽²⁾		—		6,018		—		6,018
Total financial assets	$	98,510	$	6,018	$	—	$	104,528

(1)	Included in cash and cash equivalents on the accompanying condensed consolidated balance sheets.

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

	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 the accompanying condensed consolidated balance sheets.

Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2020

Investments All Other Investments [Abstract]

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

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

March 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	70,364	$	—	$	—	$	70,364
U.S. government agency securities		28,026		120		—		28,146
Federal agency securities		5,998		20		—		6,018
Total financial assets	$	104,388	$	140	$	—	$	104,528
Classified as:
Cash and cash equivalents							$	70,364
Short-term investments								34,164
							$	104,528

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

Lease (Tables)

3 Months Ended

Mar. 31, 2020

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:

March 31, 2020

December 31, 2019

Weighted-average remaining lease

term

3.08 years

3.33 years

Weighted-average discount rate

6.0

Schedule of Maturity of Operating Lease Liabilities

The maturity of the Company’s operating lease liabilities as of March 31, 2020 were as follows (in thousands):

Remaining in 2020	$	435
2021		596
2022		613
2023		209
Total undiscounted lease payments		1,853
Less imputed interest		(167	)
Total operating lease liability	$	1,686

Schedule of Supplemental Cash Flow Information

Supplemental cash flow information related to operating leases was as follows (in thousands):

Three Months Ended March 31,

2020

2019

Cash paid for leases that were

included in operating cash outflows

142

138

Stock Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

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)
Outstanding — December 31, 2019		1,577,541		$	10.85		8.15
Options granted		469,750		$	6.87
Options exercised		(44,605	)	$	5.04
Options forfeited		(26,116	)	$	16.04
Options expired		(3,918	)	$	67.12
Outstanding — March 31, 2020		1,972,652		$	9.86		8.13
Exercisable — March 31, 2020		808,220		$	12.50

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 three months ended March 31, 2020 and 2019:

	Three Months Ended March 31,
	2020			2019
Employee Stock Options:
Risk-free interest rate		1.57	%		2.56	%
Expected term (in years)		5.53			6.03
Dividend yield		—			—
Volatility		110.00	%		82.91	%
Weighted-average fair value of stock options granted	$	5.58		$	5.80

Summary of Stock-Based Compensation Recognized

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

	Three Months Ended March 31,
	2020		2019
Research and development	$	344	$	238
General and administrative⁽¹⁾		461		591
Total stock-based compensation	$	805	$	829

(1)	Included in general and administrative stock-based compensation for the three months ended March 31, 2020 is expense related to 7,817 shares of common stock issued to certain board members in lieu of their cash compensation.

Net Loss per Share Attributable to Common Stockholders (Tables)

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Basic and Diluted Net Loss Per Common Share

	Three Months Ended March 31,
	2020			2019
Net loss attributable to common stockholders	$	(4,053	)	$	(15,083	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		14,592,451			11,963,586
Net loss available for common stockholders per share, basic and diluted	$	(0.28	)	$	(1.26	)

Anti-dilutive Security not Included In Diluted per Share Calculations

	Three Months Ended March 31,
	2020		2019
Options to purchase common stock		1,972,652		1,612,871
Common stock warrants		7,857		10,194
Total		1,980,509		1,623,065

Interest and Other Income, Net (Tables)

3 Months Ended

Mar. 31, 2020

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 three months ended March 31, 2020 and 2019 (in thousands):

	Three Months Ended March 31,
	2020		2019
Interest income	$	334	$	631
Miscellaneous income		679		—
Other		2		—
Total interest and other income, net	$	1,015	$	631

Nature of Operations and Liquidity - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) Segment	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Number of operating segment \| Segment	1
Net loss	$ 4,053	$ 15,083
Accumulated deficit	262,573		$ 258,520
Cash, cash equivalents and short-term investments	$ 104,500

- Definition

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

+ References + Details

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

Mar. 31, 2020

Dec. 31, 2019

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

Assets, fair value

$ 104,528

$ 76,865

Money Market Funds

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

Assets, fair value

^[1]

70,364

15,369

U.S. Government Agency Securities

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

Assets, fair value

^[2]

28,146

51,490

Federal Agency Securities | Short-Term Investments

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

Assets, fair value

^[2]

6,018

10,006

Fair Value, Inputs, Level 1

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

Assets, fair value

98,510

66,859

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]

70,364

15,369

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

^[2]

28,146

51,490

Fair Value, Inputs, Level 2

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

Assets, fair value

6,018

10,006

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

^[2]

$ 6,018

$ 10,006

[1]	Included in cash and cash equivalents on the accompanying condensed consolidated balance sheets.
[2]	Included in short-term investments on the accompanying condensed consolidated balance sheets and classified as available-for-sale debt securities.

Cash Equivalents and Short-Term Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 104,388	$ 76,831
Gross Unrealized Gains	140	34
Estimated Fair Value	104,528	76,865
Money Market Funds \| Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	70,364	15,369
Estimated Fair Value	70,364	15,369
U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	28,026	51,467
Gross Unrealized Gains	120	23
Estimated Fair Value	28,146	51,490
Cash and Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	70,364	15,369
Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	34,164	61,496
Federal Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,998	9,995
Gross Unrealized Gains	20	11
Estimated Fair Value	$ 6,018	$ 10,006

Financial Instruments - Additional Information (Detail)	3 Months Ended
Financial Instruments - Additional Information (Detail)	Mar. 31, 2020 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

Lease - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lessee Disclosure [Abstract]
Lease expiration date	Apr. 30, 2023
Lessee operating lease renewal term description	no stated renewal options
Operating lease expense	$ 0.2	$ 0.2

Summary of Present Value Assumptions used in Calculating Present Value of Lease Payments (Detail)	Mar. 31, 2020	Dec. 31, 2019
Lessee Disclosure [Abstract]
Weighted-average remaining lease term	3 years 29 days	3 years 3 months 29 days
Weighted-average discount rate	6.00%	6.00%

Schedule of Maturity of Operating Lease Liabilities (Detail) $ in Thousands	Mar. 31, 2020 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Remaining in 2020	$ 435
2021	596
2022	613
2023	209
Total undiscounted lease payments	1,853
Less imputed interest	(167)
Total operating lease liability	$ 1,686

Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Lease Liabilities Payments Due [Abstract]
Cash paid for leases that were included in operating cash outflows	$ 142	$ 138

Summary of Option Activity Under Company's Equity Incentive Plans (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance	1,577,541
Number of Shares Underlying Outstanding Options, Options granted	469,750
Number of Shares Underlying Outstanding Options, Options exercised	(44,605)
Number of Shares Underlying Outstanding Options, Options forfeited	(26,116)
Number of Shares Underlying Outstanding Options, Options expired	(3,918)
Number of Shares Underlying Outstanding Options, Ending Balance	1,972,652	1,577,541
Number of Shares Underlying Outstanding Options, Exercisable - March 31, 2020	808,220
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance	$ 10.85
Weighted- Average Exercise Price, Options granted	6.87
Weighted- Average Exercise Price, Options exercised	5.04
Weighted- Average Exercise Price, Options forfeited	16.04
Weighted- Average Exercise Price, Options expired	67.12
Weighted- Average Exercise Price, Ending Balance	9.86	$ 10.85
Weighted- Average Exercise Price, Exercisable - March 31, 2020	$ 12.50
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	8 years 1 month 17 days	8 years 1 month 24 days

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock issued to certain board members in lieu of cash compensation	7,817
Number of common stock available for future grant	276,043
Shares remaining outstanding	1,972,652		1,577,541
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of stock options	5 years 6 months 10 days	6 years 10 days
Unrecognized employee stock based compensation expense	$ 7.1
Unrecognized employee stock based compensation expense, period for recognition	2 years 7 months 13 days

Fair Values of Stock Options Estimated Using Black-Scholes Valuation Model (Detail) - Employee Stock Option - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Risk-free interest rate	1.57%	2.56%
Expected term (in years)	5 years 6 months 10 days	6 years 10 days
Dividend yield	0.00%	0.00%
Volatility	110.00%	82.91%
Weighted-average fair value of stock options granted	$ 5.58	$ 5.80

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

3 Months Ended

Mar. 31, 2020

Mar. 31, 2019

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

Total stock-based compensation

$ 805

$ 829

Research and development

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

Total stock-based compensation

344

238

General and Administrative

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

Total stock-based compensation

^[1]

$ 461

$ 591

[1]	Included in general and administrative stock-based compensation for the three months ended March 31, 2020 is expense related to 7,817 shares of common stock issued to certain board members in lieu of their cash compensation.

Collaborations - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended
	Jan. 31, 2020	Dec. 31, 2018	Feb. 28, 2018	Mar. 31, 2020	Dec. 08, 2016
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue				$ 16,366,000
License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue				15,045,000
Exclusive License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue				100,000
Collaboration
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue				1,321,000
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 certain 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		0
ISU Abxis \| Amended and Restated License Agreement \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment		19,500,000		0
Commercial milestone payments		$ 17,000,000		$ 0
Biogen \| License and Collaboration Agreement (the “Biogen Agreement”)
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research services				30 months
Research services option to extend				12 months
Biogen \| Exclusive License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Up-front payments received	$ 15,000,000
Biogen \| Exclusive License \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Development and sales milestone payments	$ 340,000,000

Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (4,053)	$ (15,083)
Weighted-average number of shares used in computing net loss per share, basic and diluted	14,592,451	11,963,586
Net loss available for common stockholders per share, basic and diluted	$ (0.28)	$ (1.26)

Anti-dilutive Security not Included In Diluted per Share Calculations (Detail) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,980,509	1,623,065
Options To Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,972,652	1,612,871
Common Stock Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	7,857	10,194

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Feb. 29, 2020	Mar. 31, 2020
Stockholders Equity Disclosure [Line Items]
Net proceeds from sale of common stock after deducting underwriting commissions and offering expenses payable	$ 32.0
Underwriting discounts, commissions and offering expenses payable	$ 2.5
Common Stock
Stockholders Equity Disclosure [Line Items]
Firm commitment underwritten public offering shares	5,307,692
Issuance of stock, shares		5,307,692
Common stock price, per share	$ 6.50
Common Stock \| Overallotment Option
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	692,307

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Mar. 31, 2020 USD ($)
AGC Biologics, Inc \| Marzeptacog Alfa Activated and Dalcinonacog Alfa
Commitments And Contingencies Disclosure [Line Items]
Firm work order supporting clinical trials	$ 10.7
Contractual obligation payments	3.4
Catalent Indiana, LLC. \| Dalcinonacog alfa.
Commitments And Contingencies Disclosure [Line Items]
Firm work order supporting clinical trials	0.5
Contractual obligation payments	$ 0.4

Related Parties - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 10, 2020
License and Collaboration Agreement (the “Biogen Agreement”)
Related Party Transaction [Line Items]
Upfront license fee received from collaboration agreement			$ 15.0
Mosaic
Related Party Transaction [Line Items]
Payment related to collaboration	$ 3.0
Mosaic \| Collaboration Agreement \| Intravitreal Anti-Complement Factor 3
Related Party Transaction [Line Items]
Expenses related to collaboration	$ 0.7	$ 0.3

Detail of Interest and Other Income, Net (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other Income And Expenses [Abstract]
Interest income	$ 334	$ 631
Miscellaneous income	679
Other	2
Total interest and other income, net	$ 1,015	$ 631

Subsequent Event - Additional Information (Detail) - Subsequent Event - Mosaic - Collaboration Agreement	May 08, 2020 USD ($)
Subsequent Event [Line Items]
One time expense related to collaboration	$ 750,000
Maximum
Subsequent Event [Line Items]
Milestone payments , clinical development events	$ 4,000,000