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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Jul. 26, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
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		12,015,921
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	000-51173
Entity Tax Identification Number	562020050
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	California
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	871-0761

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 17,348	$ 31,213
Short-term investments	76,587	88,914
Restricted cash	50	50
Prepaid and other current assets	4,072	3,814
Total current assets	98,057	123,991
Other assets, noncurrent	257	543
Right-of-use assets	2,188
Property and equipment, net	371	386
Total assets	100,873	124,920
Current liabilities:
Accounts payable	393	1,248
Accrued compensation	1,410	1,495
Other accrued liabilities	3,932	2,043
Deferred rent, current portion		15
Operating lease liability	461
Total current liabilities	6,196	4,801
Operating lease liability, noncurrent	1,566
Deferred rent, noncurrent portion		174
Total liabilities	7,762	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; 12,008,528 and 11,954,528 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	12	12
Additional paid-in capital	325,246	323,279
Accumulated other comprehensive income (loss)	57	(4)
Accumulated deficit	(232,204)	(203,342)
Total stockholders’ equity	93,111	119,945
Total liabilities and stockholders’ equity	$ 100,873	$ 124,920

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
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	12,008,528	11,954,528
Common stock, shares outstanding	12,008,528	11,954,528

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Contract revenue				$ 6
Type of Revenue [Extensible List]	cbio:ContractMember	cbio:ContractMember	cbio:ContractMember	cbio:ContractMember
Operating expenses:
Research and development	$ 11,111	$ 3,889	$ 23,138	$ 7,660
General and administrative	3,270	3,225	6,956	6,139
Total operating expenses	14,381	7,114	30,094	13,799
Loss from operations	(14,381)	(7,114)	(30,094)	(13,793)
Interest and other income, net	601	632	1,232	2,269
Net loss	$ (13,780)	$ (6,482)	$ (28,862)	$ (11,524)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.15)	$ (0.54)	$ (2.41)	$ (1.10)
Shares used to compute net loss per share attributable to common stockholders, basic and diluted	11,989,866	11,938,401	11,976,799	10,472,180

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (13,780)	$ (6,482)	$ (28,862)	$ (11,524)
Other comprehensive income (loss):
Unrealized gain on available-for-sale securities	44	8	61	4
Total comprehensive loss	$ (13,736)	$ (6,474)	$ (28,801)	$ (11,520)

- 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	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	606			606
Issuance of common stock for secondary public offering, net of issuance costs	106,762		$ 4	106,758
Issuance of common stock for secondary public 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 option exercises, shares			59
Conversion of redeemable convertible notes to common stock, value	3			3
Conversion of redeemable convertible notes to common stock, shares			21
Unrealized gain on available-for-sale securities	(4)				$ (4)
Net loss	(5,042)					(5,042)
Balance at Mar. 31, 2018	142,851		$ 12	321,172	(4)	(178,329)
Balance (in shares) at Mar. 31, 2018			11,935,081
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)
Unrealized gain on available-for-sale securities	4
Net loss	(11,524)
Balance at Jun. 30, 2018	136,963		$ 12	321,758	4	(184,811)
Balance (in shares) at Jun. 30, 2018			11,942,729
Balance at Mar. 31, 2018	142,851		$ 12	321,172	(4)	(178,329)
Balance (in shares) at Mar. 31, 2018			11,935,081
Stock-based compensation expense	550			550
Issuance of common stock from option exercises	36			36
Issuance of common stock from option exercises, shares			7,648
Unrealized gain on available-for-sale securities	8				8
Net loss	(6,482)					(6,482)
Balance at Jun. 30, 2018	136,963		$ 12	321,758	4	(184,811)
Balance (in shares) at Jun. 30, 2018			11,942,729
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 securities	17				17
Net loss	(15,082)					(15,082)
Balance at Mar. 31, 2019	105,815		$ 12	324,214	13	(218,424)
Balance (in shares) at Mar. 31, 2019			11,974,104
Balance at Dec. 31, 2018	$ 119,945		$ 12	323,279	(4)	(203,342)
Balance (in shares) at Dec. 31, 2018			11,954,528
Issuance of common stock from option exercises, shares	41,219
Unrealized gain on available-for-sale securities	$ 61
Net loss	(28,862)
Balance at Jun. 30, 2019	93,111		$ 12	325,246	57	(232,204)
Balance (in shares) at Jun. 30, 2019			12,008,528
Balance at Mar. 31, 2019	105,815		$ 12	324,214	13	(218,424)
Balance (in shares) at Mar. 31, 2019			11,974,104
Stock-based compensation expense	903		$ 5,999	903
Issuance of common stock from option exercises	129			129
Issuance of common stock from option exercises, shares			28,425
Unrealized gain on available-for-sale securities	44				44
Net loss	(13,780)					(13,780)
Balance at Jun. 30, 2019	$ 93,111		$ 12	$ 325,246	$ 57	$ (232,204)
Balance (in shares) at Jun. 30, 2019			12,008,528

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

6 Months Ended

Jun. 30, 2019

Jun. 30, 2018

Operating Activities

Net loss

$ (28,862)

$ (11,524)

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

Stock-based compensation expense

1,732

1,156

Depreciation and amortization

Loss on disposal of property and equipment

116

Changes in operating assets and liabilities:

Prepaid and other current assets

(361)

(1,469)

Accounts payable

(855)

(613)

Accrued compensation and other accrued liabilities

1,803

(393)

Operating lease liability and right-of-use assets

Deferred rent

143

Deferred revenue

(6)

Net cash flows used in operating activities

(26,424)

(12,520)

Investing Activities

Proceeds from maturities of short-term investments

89,005

30,693

Purchase of short-term investments

(76,617)

(102,330)

Purchases of property and equipment

(64)

(201)

Net cash flows provided by (used in) investing activities

12,324

(71,838)

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

235

Proceeds from exercise of warrants

9,545

Net cash flow provided by financing activities

235

111,261

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

(13,865)

26,903

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

31,263

19,805

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

^[1]

17,398

46,708

Supplemental Disclosure of Non-Cash Investing and Financing Activities:

Adoption of ASC 606

207

Conversion of redeemable convertible notes to common stock

Unrealized gain on investments

$ 4

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

$ 2,052

[1]	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

Jun. 30, 2019

Dec. 31, 2018

Jun. 30, 2018

Dec. 31, 2017

Statement Of Cash Flows [Abstract]

Cash and cash equivalents

$ 17,348

$ 31,213

$ 46,533

Restricted cash

175

Total cash and restricted cash

$ 17,398

^[1]

$ 31,263

$ 46,708

^[1]

$ 19,805

[1]	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

6 Months Ended

Jun. 30, 2019

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 clinical-stage biopharmaceutical company focused on developing novel treatments for hemophilia and other rare bleeding disorders using its engineered subcutaneous (SC) coagulation factors that promote blood clotting. The Company is located in South San Francisco, California and it operates in one segment.

The Company had a net loss of $28.9 million for the six months ended June 30, 2019 and an accumulated deficit of $232.2 million as of June 30, 2019 and expects to continue to incur losses for the next several years. As of June 30, 2019, the Company had $94.0 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 June 30, 2019 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

6 Months Ended

Jun. 30, 2019

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, 2018 (“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 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. There have been no other significant changes to these accounting policies during the first six months of 2019.

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. As a result, the Company no longer recognizes deferred rent on the balance sheet.

On January 1, 2019, the Company adopted the new lease accounting standard using the optional transition method under which comparative financial information is not restated and continues to apply the provisions of the previous lease accounting standard in its financial disclosures for the comparative periods. The Company also elected relevant optional practical expedients including 1) did not reassess whether expired or existing contracts are or contain a lease, 2) did not reassess the lease classifications or reassess the initial direct costs associated with expired or existing leases, and 3) did not 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 and had no impact on cash provided by or used in operating, investing or financing activities on the Company's condensed consolidated statements of cash flows. The adoption of the new lease accounting standard did not impact previously reported financial results.

Fair Value Measurements

6 Months Ended

Jun. 30, 2019

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 six months ended June 30, 2019.

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 June 30, 2019 and December 31, 2018 (in thousands):

	June 30, 2019
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	16,858	$	—	$	—	$	16,858
U.S. government agency securities⁽²⁾		57,904				—		57,904
Federal agency securities⁽²⁾		—		18,683		—		18,683
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	74,812	$	18,683	$	—	$	93,495

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

(2)	Included in short-term investments on accompanying condensed consolidated balance sheets and are classified as available-for-sale 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
U.S. Treasury securities⁽²⁾		74,139						74,139
Federal agency securities⁽²⁾				14,775		—		14,775
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	103,279	$	15,774	$	—	$	119,053

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

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

6 Months Ended

Jun. 30, 2019

Investments All Other Investments [Abstract]

Financial Instruments

4.	Financial Instruments

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

June 30, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	16,858	$	—	$	—	$	16,858
U.S. government agency securities		57,870		34		—		57,904
Federal agency securities		18,660		23		—		18,683
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	93,438	$	57	$	—	$	93,495
Classified as:
Cash and cash equivalents							$	16,858
Short-term investments								76,587
Restricted cash (money market funds)								50
							$	93,495

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 (money market funds)		50		—		—			50
U.S. government agency securities		74,144		1		(6	)		74,139
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 (money market funds)									50
								$	119,053

There have been no material realized gains or losses on available-for-sale securities for the periods presented. As of June 30, 2019, the remaining contractual maturities of available-for-sale debt securities was less than one year.

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

Lease

6 Months Ended

Jun. 30, 2019

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 liability but are reflected as an expense in the period incurred.

For the six months ended June 30, 2019, the Company’s operating lease expense was $0.3 million. The present value assumptions used in calculating the present value of the lease payments were as follows:

Weighted-average remaining lease term				3.8 years
Weighted-average discount rate					6.0	%

Future lease payments under non-cancelable leases as of June 30, 2019 were as follows:

Remaining in 2019	$	282
2020		578
2021		596
2022		613
2023		209
Total future minimum lease payments		2,278
Less imputed interest		(251	)
Total lease liability	$	2,027

Stock Based Compensation

6 Months Ended

Jun. 30, 2019

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, 2018		1,361,977		$	12.04		8.71
Options granted		395,300		$	8.10
Options exercised		(41,219	)	$	4.57
Options forfeited		(60,290	)	$	8.14
Options expired		(7,474	)	$	74.90
Outstanding — June 30, 2019		1,648,294		$	11.14		8.60
Exercisable — June 30, 2019		547,822		$	15.74		7.95
Vested and expected to vest — June 30, 2019		1,648,294		$	11.14		8.60

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 six months ended June 30, 2019 and 2018:

	Six Months Ended June 30,
	2019			2018
Employee Stock Options:
Risk-free interest rate		2.44	%		2.48	%
Expected term (in years)		5.98			5.93
Dividend yield		—			—
Volatility		88.21	%		104.37	%
Weighted-average fair value of stock options granted	$	5.96		$	13.38

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	284	$	137	$	522	$	252
General and administrative⁽¹⁾		619		414		1,210		904
Total stock-based compensation	$	903	$	551	$	1,732	$	1,156

(1)	Included $0.03 and $0.1 million in modifications related to certain Board member stock options in the three and six months ended June 30, 2019 and for the six months ended June 30, 2018, respectively.

Also included in total stock-based compensation for the three and six months ended June 30, 2019 is expense related to 5,999 shares of common stock issued to certain board members in lieu of their cash compensation.

As of June 30, 2019, 961,609 shares of common stock were available for future grant and 1,648,294 options to purchase shares of common stock were outstanding. As of June 30, 2019, 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 2.78 years.

Collaborations

6 Months Ended

Jun. 30, 2019

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 million milestone payment based on the dosing of the first patient in its ongoing Phase 2 study; the amount was recorded as a research and development expense. No payments were made to Pfizer in the first six months of 2019.

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 million in commercial milestone payments, if the applicable milestones are met.

Net Loss per Share Attributable to Common Stockholders

6 Months Ended

Jun. 30, 2019

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 six months ended June 30, 2019 and 2018 (in thousands, except share and per share data):

	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Net loss attributable to common stockholders	$	(13,780	)	$	(6,482	)	$	(28,862	)	$	(11,524	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		11,989,866			11,938,401			11,976,799			10,472,180
Net loss available for common stockholders per share, basic and diluted	$	(1.15	)	$	(0.54	)	$	(2.41	)	$	(1.10	)

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:

	Six Months Ended June 30,
	2019		2018
Options to purchase common stock		1,648,294		1,071,899
Common stock warrants		7,857		12,039
Redeemable convertible notes		—		—
Total		1,656,151		1,083,938

Stockholders' Equity

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Stockholders' Equity

9.	Stockholders’ Equity

February 2018 Underwritten Public Offering — 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.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2019

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 $12.4 million and the payment obligations remaining at June 30, 2019 was $5.4 million.

Related Parties

6 Months Ended

Jun. 30, 2019

Related Parties

11.	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 products for the treatment of dry age-related macular degeneration and other retinal diseases. According to the agreement the Company and Mosaic will co-fund the research. Dr. Usman, the Company’s Chief Executive Officer and a member of the Company’s board of directors, and Mr. Lawlor, the chairman of the Company’s board of directors, were also members of the board of directors of Mosaic when this agreement was entered in to, and the agreement was reviewed by disinterested members of the Company’s board of directors and approved by the Company’s audit committee. Expenses related to the collaboration were $0.3 and $0.3 million for the three months ended June 30, 2019 and 2018, respectively. Expenses related to the collaboration were $0.7 and $0.5 million for the six months ended June 30, 2019 and 2018, respectively.

Interest and Other Income

6 Months Ended

Jun. 30, 2019

Other Income And Expenses [Abstract]

Interest and Other Income

12.	Interest and Other Income

The following table shows the detail of interest and other income/(expense), net for the three-and six-months ended June 30, 2019 and 2018 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019			2018
Interest income	$	601	$	602	$	1,262		$	887
Loss on disposal of fixed assets		—		—		—			(116	)
Other income/(expense), net		—		30		(30	)		1,498
Total other income/(expense), net	$	601	$	632	$	1,232		$	2,269

Other income of $1.5 million for the six months ended June 30, 2018 reflects milestone payments received under an agreement associated with neuronal nicotinic receptor assets sold in 2016.

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2019
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, 2018 (“Annual Report”).
Reclassification	Error extracting Word content
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 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. There have been no other significant changes to these accounting policies during the first six months of 2019. 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. As a result, the Company no longer recognizes deferred rent on the balance sheet. On January 1, 2019, the Company adopted the new lease accounting standard using the optional transition method under which comparative financial information is not restated and continues to apply the provisions of the previous lease accounting standard in its financial disclosures for the comparative periods. The Company also elected relevant optional practical expedients including 1) did not reassess whether expired or existing contracts are or contain a lease, 2) did not reassess the lease classifications or reassess the initial direct costs associated with expired or existing leases, and 3) did not 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 and had no impact on cash provided by or used in operating, investing or financing activities on the Company's condensed consolidated statements of cash flows. The adoption of the new lease accounting standard did not impact previously reported financial results.

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Assets and Liabilities Measured at Fair Value on a Recurring Basis

	June 30, 2019
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	16,858	$	—	$	—	$	16,858
U.S. government agency securities⁽²⁾		57,904				—		57,904
Federal agency securities⁽²⁾		—		18,683		—		18,683
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	74,812	$	18,683	$	—	$	93,495

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

(2)	Included in short-term investments on accompanying condensed consolidated balance sheets and are classified as available-for-sale 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
U.S. Treasury securities⁽²⁾		74,139						74,139
Federal agency securities⁽²⁾				14,775		—		14,775
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	103,279	$	15,774	$	—	$	119,053

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

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

Financial Instruments (Tables)

6 Months Ended

Jun. 30, 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 (debt securities) which are classified as available-for-sale securities, consisted of the following (in thousands):

June 30, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	16,858	$	—	$	—	$	16,858
U.S. government agency securities		57,870		34		—		57,904
Federal agency securities		18,660		23		—		18,683
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	93,438	$	57	$	—	$	93,495
Classified as:
Cash and cash equivalents							$	16,858
Short-term investments								76,587
Restricted cash (money market funds)								50
							$	93,495

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 (money market funds)		50		—		—			50
U.S. government agency securities		74,144		1		(6	)		74,139
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 (money market funds)									50
								$	119,053

Lease (Tables)

6 Months Ended

Jun. 30, 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				3.8 years
Weighted-average discount rate					6.0	%

Summary of Future Lease Payments under Non-cancelable Leases

Future lease payments under non-cancelable leases as of June 30, 2019 were as follows:

Remaining in 2019	$	282
2020		578
2021		596
2022		613
2023		209
Total future minimum lease payments		2,278
Less imputed interest		(251	)
Total lease liability	$	2,027

Stock Based Compensation (Tables)

6 Months Ended

Jun. 30, 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)
Outstanding — December 31, 2018		1,361,977		$	12.04		8.71
Options granted		395,300		$	8.10
Options exercised		(41,219	)	$	4.57
Options forfeited		(60,290	)	$	8.14
Options expired		(7,474	)	$	74.90
Outstanding — June 30, 2019		1,648,294		$	11.14		8.60
Exercisable — June 30, 2019		547,822		$	15.74		7.95
Vested and expected to vest — June 30, 2019		1,648,294		$	11.14		8.60

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 six months ended June 30, 2019 and 2018:

	Six Months Ended June 30,
	2019			2018
Employee Stock Options:
Risk-free interest rate		2.44	%		2.48	%
Expected term (in years)		5.98			5.93
Dividend yield		—			—
Volatility		88.21	%		104.37	%
Weighted-average fair value of stock options granted	$	5.96		$	13.38

Summary of Stock-Based Compensation Recognized

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	284	$	137	$	522	$	252
General and administrative⁽¹⁾		619		414		1,210		904
Total stock-based compensation	$	903	$	551	$	1,732	$	1,156

(1)	Included $0.03 and $0.1 million in modifications related to certain Board member stock options in the three and six months ended June 30, 2019 and for the six months ended June 30, 2018, respectively.

Net Loss per Share Attributable to Common Stockholders (Tables)

6 Months Ended

Jun. 30, 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 six months ended June 30, 2019 and 2018 (in thousands, except share and per share data):

	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Net loss attributable to common stockholders	$	(13,780	)	$	(6,482	)	$	(28,862	)	$	(11,524	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		11,989,866			11,938,401			11,976,799			10,472,180
Net loss available for common stockholders per share, basic and diluted	$	(1.15	)	$	(0.54	)	$	(2.41	)	$	(1.10	)

Anti-dilutive Security not Included In Diluted per Share Calculations

	Six Months Ended June 30,
	2019		2018
Options to purchase common stock		1,648,294		1,071,899
Common stock warrants		7,857		12,039
Redeemable convertible notes		—		—
Total		1,656,151		1,083,938

Interest and Other Income (Tables)

6 Months Ended

Jun. 30, 2019

Other Income And Expenses [Abstract]

Detail of Interest and Other Income/(Expense), Net

The following table shows the detail of interest and other income/(expense), net for the three-and six-months ended June 30, 2019 and 2018 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019			2018
Interest income	$	601	$	602	$	1,262		$	887
Loss on disposal of fixed assets		—		—		—			(116	)
Other income/(expense), net		—		30		(30	)		1,498
Total other income/(expense), net	$	601	$	632	$	1,232		$	2,269

Nature of Operations - Additional Information (Detail) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Number of operating segment \| Segment					1
Net loss	$ 13,780	$ 15,082	$ 6,482	$ 5,042	$ 28,862	$ 11,524
Accumulated deficit	232,204				232,204		$ 203,342
Cash, cash equivalents, and short-term investments	$ 94,000				$ 94,000

- Definition

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

+ References + Details

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Accounting Standards Update 2016-02 Leases (Topic 842)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impact of new lease accounting standard on assets and liabilities	$ 2.1

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

Jun. 30, 2019

Dec. 31, 2018

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

Assets, fair value

$ 93,495

$ 119,053

Money Market Funds

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

Assets, fair value

^[1]

16,858

29,090

Restricted cash (money market funds)

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

Assets, fair value

U.S. Government Agency Securities

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

Assets, fair value

^[2]

57,904

Federal Agency Securities | Short-Term Investments

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

Assets, fair value

^[2]

18,683

14,775

Federal Agency Securities | Cash and Cash Equivalents

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

Assets, fair value

^[1]

999

US Treasury Securities | Short-Term Investments

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

Assets, fair value

^[2]

74,139

Fair Value, Inputs, Level 1

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

Assets, fair value

74,812

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]

16,858

29,090

Fair Value, Inputs, Level 1 | Restricted cash (money market funds)

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

Assets, fair value

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]

57,904

Fair Value, Inputs, Level 1 | US Treasury Securities | Short-Term Investments

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

Assets, fair value

^[2]

74,139

Fair Value, Inputs, Level 2

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

Assets, fair value

18,683

15,774

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]

$ 18,683

14,775

Fair Value, Inputs, Level 2 | Federal Agency Securities | Cash and Cash Equivalents

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

Assets, fair value

^[1]

$ 999

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

Cash Equivalents, Restricted Cash and Short-Term Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 93,438	$ 119,057
Gross Unrealized Gains	57	2
Gross Unrealized Losses		(6)
Estimated Fair Value	93,495	119,053
Money Market Funds \| Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,858	29,090
Estimated Fair Value	16,858	29,090
Money Market Funds \| Restricted cash
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50	50
Estimated Fair Value	50	50
U.S. Government Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,870	74,144
Gross Unrealized Gains	34	1
Gross Unrealized Losses		(6)
Estimated Fair Value	57,904	74,139
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	16,858	30,089
Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	76,587	88,914
Federal Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,660
Gross Unrealized Gains	23
Estimated Fair Value	$ 18,683
Federal Agency Securities \| Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		999
Estimated Fair Value		999
Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		14,774
Gross Unrealized Gains		1
Estimated Fair Value		$ 14,775

Financial Instruments - Additional Information (Detail)	6 Months Ended
Financial Instruments - Additional Information (Detail)	Jun. 30, 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

Lease - Additional Information (Detail) $ in Millions	6 Months Ended
Lease - Additional Information (Detail) $ in Millions	Jun. 30, 2019 USD ($)
Lessee Disclosure [Abstract]
Lease expiration date	Apr. 30, 2023
Lessee operating lease renewal term description	no stated renewal options
Operating lease expense	$ 0.3

Summary of Present Value Assumptions used in Calculating Present Value of Lease Payments (Detail)	Jun. 30, 2019
Lessee Disclosure [Abstract]
Weighted-average remaining lease term	3 years 9 months 18 days
Weighted-average discount rate	6.00%

Summary of Future Lease Payments under Non-cancelable Leases (Detail)	Jun. 30, 2019 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Remaining in 2019	$ 282
2020	578
2021	596
2022	613
2023	209
Total future minimum lease payments	2,278
Less imputed interest	(251)
Total lease liability	$ 2,027

Summary of Option Activity Under Company's Equity Incentive Plans (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance \| shares	1,361,977
Number of Shares Underlying Outstanding Options, Options granted \| shares	395,300
Number of Shares Underlying Outstanding Options, Options exercised \| shares	(41,219)
Number of Shares Underlying Outstanding Options, Options forfeited \| shares	(60,290)
Number of Shares Underlying Outstanding Options, Options expired \| shares	(7,474)
Number of Shares Underlying Outstanding Options, Ending Balance \| shares	1,648,294	1,361,977
Number of Shares Underlying Outstanding Options, Exercisable - June 30, 2019 \| shares	547,822
Number of Shares Underlying Outstanding Options, Vested and expected to vest - June 30, 2019 \| shares	1,648,294
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance \| $ / shares	$ 12.04
Weighted- Average Exercise Price, Options granted \| $ / shares	8.10
Weighted- Average Exercise Price, Options exercised \| $ / shares	4.57
Weighted- Average Exercise Price, Options forfeited \| $ / shares	8.14
Weighted- Average Exercise Price, Options expired \| $ / shares	74.90
Weighted- Average Exercise Price, Ending Balance \| $ / shares	11.14	$ 12.04
Weighted- Average Exercise Price, Exercisable - June 30, 2019 \| $ / shares	15.74
Weighted- Average Exercise Price, Vested and expected to vest - June 30, 2019 \| $ / shares	$ 11.14
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	8 years 7 months 6 days	8 years 8 months 15 days
Weighted-Average Remaining Contractual Term (Years), Exercisable - June 30, 2019	7 years 11 months 12 days
Weighted-Average Remaining Contractual Term (Years), Vested and expected to vest - June 30, 2019	8 years 7 months 6 days

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018
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	5,999
Number of common stock available for future grant	961,609	961,609
Shares remaining outstanding	1,648,294	1,648,294
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of stock options		5 years 11 months 23 days	5 years 11 months 4 days
Unrecognized employee stock based compensation expense	$ 7.1	$ 7.1
Unrecognized employee stock based compensation expense, period for recognition		2 years 9 months 10 days

Fair Values of Stock Options Estimated Using Black-Scholes Valuation Model (Detail) - Employee Stock Option - $ / shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Risk-free interest rate	2.44%	2.48%
Expected term (in years)	5 years 11 months 23 days	5 years 11 months 4 days
Dividend yield	0.00%	0.00%
Volatility	88.21%	104.37%
Weighted-average fair value of stock options granted	$ 5.96	$ 13.38

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

3 Months Ended

6 Months Ended

Jun. 30, 2019

Jun. 30, 2018

Jun. 30, 2019

Jun. 30, 2018

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

Total stock-based compensation

$ 903

$ 551

$ 1,732

$ 1,156

Research and development

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

Total stock-based compensation

284

137

522

252

General and Administrative

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

Total stock-based compensation

^[1]

$ 619

$ 414

$ 1,210

$ 904

[1]	Included $0.03 and $0.1 million in modifications related to certain Board member stock options in the three and six months ended June 30, 2019 and for the six months ended June 30, 2018, respectively.

Summary of Stock-Based Compensation Recognized (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Modification of stock options, expense	$ 903	$ 551	$ 1,732	$ 1,156
Board Member Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Modification of stock options, expense	$ 30		$ 30	$ 100

Collaborations - Additional Information (Detail) - USD ($)	1 Months Ended		6 Months Ended
	Dec. 31, 2018	Feb. 28, 2018	Jun. 30, 2019	Dec. 08, 2016
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
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

Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (13,780)	$ (6,482)	$ (28,862)	$ (11,524)
Weighted-average number of shares used in computing net loss per share, basic and diluted	11,989,866	11,938,401	11,976,799	10,472,180
Net loss available for common stockholders per share, basic and diluted	$ (1.15)	$ (0.54)	$ (2.41)	$ (1.10)

Anti-dilutive Security not Included In Diluted per Share Calculations (Detail) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,656,151	1,083,938
Options To Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,648,294	1,071,899
Common Stock Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	7,857	12,039

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Feb. 15, 2018	Feb. 13, 2018	Mar. 31, 2018
Stockholders Equity Disclosure [Line Items]
Net proceeds from sale of common stock	$ 106.8
Common Stock
Stockholders Equity Disclosure [Line Items]
Firm commitment underwritten public offering shares		2,941,176
Issuance of stock, shares	3,382,352		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

Commitments and Contingencies - Additional Information (Detail) - AGC Biologics, Inc - Marzeptacog Alfa Activated and Dalcinonacog Alfa $ in Millions	Jun. 30, 2019 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Clinical trials	$ 12.4
Contractual obligation payments	$ 5.4

Related Parties - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Mosaic \| Strategic Research Collaboration to Develop Intravitreal Anti-Complement Factor 3 Products
Related Party Transaction [Line Items]
Expenses related to collaboration	$ 0.3	$ 0.3	$ 0.7	$ 0.5

Detail of Interest and Other Income/(Expense), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Income And Expenses [Abstract]
Interest income	$ 601	$ 602	$ 1,262	$ 887
Loss on disposal of fixed assets				(116)
Other income/(expense), net		30	(30)	1,498
Total other income/(expense), net	$ 601	$ 632	$ 1,232	$ 2,269

Interest and Other Income - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Income And Expenses [Abstract]
Other income reflects milestone payments received	$ 30	$ (30)	$ 1,498