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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	CBIO
Entity Registrant Name	CATALYST BIOSCIENCES, INC.
Entity Central Index Key	0001124105
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		4,310,561

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 10,973	$ 10,264
Short-term investments	16,477	6,800
Restricted cash	5,727	19,468
Accounts receivable	52	31
Prepaid and other current assets	849	958
Total current assets	34,078	37,521
Restricted cash, noncurrent		125
Property and equipment, net	315	444
Total assets	34,393	38,090
Current liabilities:
Accounts payable	1,460	837
Accrued compensation	920	596
Other accrued liabilities	1,095	805
Deferred revenue, current portion	530	283
Deferred rent, current portion	18	41
Redeemable convertible notes	5,488	19,403
Total current liabilities	9,511	21,965
Deferred revenue, noncurrent portion		47
Deferred rent, noncurrent portion		7
Total liabilities	9,511	22,019
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized; 5,500 and 0 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively
Common stock, $0.001 par value, 100,000,000 shares authorized; 4,310,561 and 801,756 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	4	1
Additional paid-in capital	192,615	164,053
Accumulated other comprehensive income (loss)	4	(1)
Accumulated deficit	(167,741)	(147,982)
Total stockholders’ equity	24,882	16,071
Total liabilities and stockholders’ equity	$ 34,393	$ 38,090

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
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	5,500	0
Preferred stock, shares outstanding	5,500	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	4,310,561	801,756
Common stock, shares outstanding	4,310,561	801,756

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Contract revenue	$ 318	$ 109	$ 700	$ 328
Operating expenses:
Research and development	3,805	3,396	9,286	8,443
General and administrative	2,391	2,425	7,407	7,083
Total operating expenses	6,196	5,821	16,693	15,526
Loss from operations	(5,878)	(5,712)	(15,993)	(15,198)
Interest and other income, net	85	941	185	2,003
Net loss	(5,793)	(4,771)	(15,808)	(13,195)
Deemed dividend for convertible preferred stock beneficial conversion feature			(3,951)
Net loss attributable to common stockholders	$ (5,793)	$ (4,771)	$ (19,759)	$ (13,195)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.34)	$ (6.04)	$ (6.49)	$ (17.10)
Shares used to compute net loss per share attributable to common stockholders, basic and diluted	4,310,561	789,796	3,043,919	771,713

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (5,793)	$ (4,771)	$ (15,808)	$ (13,195)
Other comprehensive income (loss):
Unrealized gain on available-for-sale securities	4	3	5	3
Total comprehensive loss	$ (5,789)	$ (4,768)	$ (15,803)	$ (13,192)

Condensed Consolidated Statement of Stockholders Equity (Unaudited) - 9 months ended Sep. 30, 2017 - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2016	$ 16,071		$ 1	$ 164,053	$ (1)	$ (147,982)
Balance (in shares) at Dec. 31, 2016			801,756
Stock-based compensation expense	556			556
Issuance of common stock, net of issuance costs	5,336		$ 1	5,335
Issuance of common stock, net of issuance costs, shares			439,880
Issuance of convertible preferred stock, common stock and warrants for follow-on offering, net of issuance costs	18,563		$ 2	18,561
Issuance of convertible preferred stock, common stock and warrants for follow-on offering, net of issuance costs, shares		13,350	1,470,000
Issuance of common stock upon exercise of warrants	159			159
Issuance of common stock upon exercise of warrants, shares			28,925
Conversion of preferred stock to common stock		(7,850)	1,570,000
Deemed dividend for preferred stock beneficial conversion feature				3,951		(3,951)
Unrealized gain on available-for-sale securities	5				5
Net loss	(15,808)					(15,808)
Balance at Sep. 30, 2017	$ 24,882		$ 4	$ 192,615	$ 4	$ (167,741)
Balance (in shares) at Sep. 30, 2017		5,500	4,310,561

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities
Net loss	$ (15,808,000)	$ (13,195,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	556,000	505,000
Depreciation and amortization	132,000	328,000
Gain on extinguishment of redeemable convertible notes	0	(92,000)
Change in fair value of derivative liability		(1,036,000)
Changes in operating assets and liabilities:
Accounts receivable	(20,000)	391,000
Prepaid and other current assets	109,000	484,000
Accounts payable	623,000	(410,000)
Accrued compensation and other accrued liabilities	614,000	(127,000)
Deferred rent	(29,000)	(14,000)
Deferred revenue	200,000	(329,000)
Net cash flows used in operating activities	(13,623,000)	(13,495,000)
Investing Activities
Proceeds from maturities of short-term investments	6,800,000	6,601,000
Purchase of investments	(16,474,000)	(13,404,000)
Change in restricted cash	(49,000)
Purchases of property and equipment	(3,000)	(346,000)
Net cash flows used in investing activities	(9,726,000)	(7,149,000)
Financing Activities
Release of restricted cash due to conversion and redemption of redeemable convertible notes	13,915,000	4,075,000
Payments for the redemption of redeemable convertible notes	(13,915,000)	(4,075,000)
Proceeds from issuance of common stock, net of issuance costs	5,336,000	865,000
Proceeds from issuance of preferred stock, common stock and warrants for follow-on offering, net of issuance costs	18,563,000
Proceeds from exercise of warrants	159,000
Net cash flows provided by financing activities	24,058,000	865,000
Net increase (decrease) in cash and cash equivalents	709,000	(19,779,000)
Cash and cash equivalents at beginning of period	10,264,000	29,096,000
Cash and equivalents at end of period	10,973,000	9,317,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Deemed dividend for convertible preferred stock beneficial conversion feature	$ 3,951,000
Conversion of convertible notes to common stock		$ 1,000

Nature of Operations

9 Months Ended

Sep. 30, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Operations

1.	Nature of Operations

Catalyst Biosciences, Inc. (the “Company” or “Catalyst”) is a clinical-stage biotechnology company focused on developing novel medicines to address hematology indications, including the treatment of hemophilia. Its facilities are in South San Francisco, California and it operates in one segment. Prior to August 20, 2015, the name of the Company was Targacept, Inc. (“Targacept”). On August 20, 2015, Targacept completed its business combination with Catalyst (the “Merger”).

On February 10, 2017, the Company effected a reverse stock split of its common stock at a ratio of 1-for-15 (“2017 Reverse Stock Split”). The 2017 Reverse Stock Split was approved by the Company’s stockholders at a special meeting of stockholders held on February 2, 2017. As a result of the 2017 Reverse Stock Split, each 15 pre-split shares of common stock outstanding were automatically combined into one new share of common stock, and the number of outstanding shares of common stock on the date of the split was reduced from approximately 13.0 million shares to approximately 868,000 shares. Unless otherwise specified, all share and per share amounts in these notes and the accompanying condensed consolidated financial statements are reported on a post-stock split basis for all periods presented.

Based on the current status of its research and development plans, the Company believes that its existing cash, cash equivalents and investments as of September 30, 2017 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

9 Months Ended

Sep. 30, 2017

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 U.S. 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, 2016 (“Annual Report”).

The Company’s significant accounting policies are included in “Part II - Item 8 - Financial Statements and Supplementary Data - Note 2 – Summary of Significant Accounting Policies” in the Company’s Annual Report. There have been no significant changes to these accounting policies during the first nine months of 2017.

Fair Value Measurements

9 Months Ended

Sep. 30, 2017

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 nine months ended September 30, 2017. As of September 30, 2017 and December 31, 2016, the Company’s highly liquid money market funds included within cash equivalents, restricted cash and U.S. government agency securities are valued using Level 1 inputs. The Company classifies its federal agency securities as Level 2. There were no transfers in or out of Level 1 and Level 2 during the periods presented.

Liabilities that are measured at fair value consist of the derivative liability associated with the redeemable convertible notes (see Note 5) and are valued using Level 3 inputs. There were no transfers in or out of Level 3 during the periods presented.

As of September 30, 2017 and December 31, 2016 the fair value of the derivative liability was immaterial. The estimated reporting date fair value-based measurement of the derivative liability was calculated using the Black-Scholes valuation model.

The following tables present the fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 (in thousands):

	September 30, 2017
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	10,973	$	—	$	—	$	10,973
U.S. government agency securities⁽³⁾		14,981	$	—	$	—		14,981
Restricted cash (money market funds)⁽²⁾		5,727		—		—		5,727
Agency securities⁽³⁾		—		1,496		—		1,496
Total financial assets	$	31,681	$	1,496	$	—	$	33,177

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

(2)	$5.5 million of restricted cash in the Indenture serves as full collateral for the redeemable convertible notes and $0.1 million of restricted cash serves as collateral for the Company’s corporate credit card and deposit for its facility lease.

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

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	10,156	$	—	$	—	$	10,156
Restricted cash (money market funds)⁽²⁾		19,593		—		—		19,593
U.S. government agency securities⁽³⁾		6,800		—		—		6,800
Total financial assets	$	36,549	$	—	$	—	$	36,549

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

(2)	$19.4 million of restricted cash in the Indenture serves as full collateral for the redeemable convertible notes and $0.1 million of restricted cash serves as collateral for the Company’s corporate credit card and deposit for its facility lease.

(3)	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

9 Months Ended

Sep. 30, 2017

Investments All Other Investments [Abstract]

Financial Instruments

4.	Financial Instruments

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

September 30, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	10,973	$	—	$	—		$	10,973
U.S. government agency securities		14,980		2		(1	)		14,981
Restricted cash (money market funds)		5,727		—		—			5,727
Agency securities		1,495		1		—			1,496
Total financial assets	$	33,175	$	3	$	(1	)	$	33,177
Classified as:
Cash and cash equivalents								$	10,973
Short-term investments									16,477
Restricted cash (money market funds)									5,727
								$	33,177

December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	10,156	$	—	$	—		$	10,156
Restricted cash (money market funds)		19,593		—		—			19,593
U.S. government agency securities		6,802		—		(2	)		6,800
Total financial assets	$	36,551	$	—	$	(2	)	$	36,549
Classified as:
Cash and cash equivalents								$	10,156
Restricted cash (money market funds)									19,593
Short-term investments									6,800
								$	36,549

There have been no significant realized gains or losses on available-for-sale securities for the periods presented. The carrying amounts of cash, accounts receivable, other receivables, accounts payable, other payables and redeemable convertible notes approximate their fair values due to the short-term maturity of these instruments.

Redeemable Convertible Notes

9 Months Ended

Sep. 30, 2017

Debt Disclosure [Abstract]

Redeemable Convertible Notes

5.	Redeemable Convertible Notes

On August 19, 2015, immediately prior to the Merger, the Company issued to Targacept stockholders non-interest bearing redeemable convertible notes (the “Notes”) in the aggregate principal amount of $37.0 million. The Notes do not bear interest. The principal amount of the Notes is convertible, at the option of each noteholder, into cash or into shares of the Company’s common stock at a conversion rate of $137.85 per share, and are payable in cash, if not previously redeemed or converted, at maturity on February 19, 2018, the 30-month anniversary of the closing of the issuance of the Notes.

In connection with the issuance of the Notes, on August 19, 2015, Targacept entered into an indenture (the “Indenture”) with American Stock Transfer & Trust Company, LLC, as trustee, and an escrow agreement with American Stock Transfer & Trust Company, LLC and Delaware Trust Company, LLC, as escrow agent, under which $37.0 million, which represented the initial principal amount of the Notes, was deposited in a segregated escrow account for the benefit of the holders of the Notes in order to facilitate the payment of the notes upon redemption or at maturity (the amount of such deposit together with interest accrued and capitalized thereon, the “Escrow Funds”). The Notes are the Company’s secured obligation, and the Indenture does not limit its other indebtedness, secured or unsecured.

Holders of the Notes may submit conversion notices, which are irrevocable, instructing the trustee to convert such Notes into shares of common stock at a conversion price of $137.85 per share. Following each conversion date, the Company will issue the number of whole shares of common stock issuable upon conversion as promptly as practicable (and in any event within 10 business days). The trustee will in turn release to the Company the respective amount of restricted cash to cover the stock issuance.

The conversion to common stock feature of the Notes was determined to be a derivative liability requiring bifurcation and separate accounting. The fair value of such conversion feature at issuance was determined to be $1.5 million. The bifurcation of the derivative liability from the estimated fair value of the Notes of $37.1 million at issuance resulted in a debt discount of $1.4 million. The Company elected to accrete the entire debt discount as interest expense immediately after the Merger. In addition, changes in the fair value of the derivative liability are being recorded within interest and other income in the consolidated statements of operations. The Company remeasures the derivative liability to fair value until the earlier of the conversion, redemption or maturity of the redeemable convertible notes.

As of September 30, 2017 and December 31, 2016, the fair value of the derivative liability was immaterial. The estimated reporting date fair value-based measurement of the derivative liability was calculated using the Black-Scholes valuation model.

The Company recognized no interest expense for both the three and nine months ended September 30, 2017 and 2016, related to the amortization of the debt discount on the Company’s consolidated statement of operations as the redeemable convertible notes are immediately fully redeemable at the option of the holders and the entire debt discount was accreted immediately after the Merger.

As of September 30, 2017, the Notes had a balance of $5.5 million, $31.2 million of the Notes were redeemed and $0.3 million of the Notes were converted into common stock. $13.9 million of the Notes were redeemed during the nine months ended September 30, 2017. There was no gain on the extinguishment of Notes upon the redemption of the Notes during the three and nine months ended September 30, 2017.

Stock Based Compensation

9 Months Ended

Sep. 30, 2017

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, 2016		140,990		$	127.56		3.93
Options granted		692,000		$	4.54
Options canceled		(141	)	$	41.91
Options forfeited		(60,854	)	$	165.77
Outstanding — September 30, 2017		771,995		$	14.30		9.37
Exercisable — September 30, 2017		106,953		$	64.96		7.10
Vested and expected to vest — September 30, 2017		771,995		$	14.30		9.37

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 5.99 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 nine months ended September 30, 2017 and 2016:

	Nine Months Ended September 30,
	2017			2016
Employee Stock Options:
Risk-free interest rate		2.02	%		1.41	%
Expected term (in years)		5.99			5.92
Dividend yield		—			—
Volatility		110.42	%		75.04	%
Weighted-average fair value of stock options granted	$	3.79		$	16.05

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development	$	62	$	68	$	97	$	172
General and administrative		263		120		459		333
Total stock-based compensation	$	325	$	188	$	556	$	505

As of September 30, 2017, 404,632 shares of common stock were available for future grant and 771,995 options to purchase shares of common stock were outstanding, additionally as of September 30, 2017 the Company had unrecognized employee stock-based compensation expense of $3.1 million, related to unvested stock awards, which is expected to be recognized over an estimated weighted-average period of 3.10 years.

Collaborations

9 Months Ended

Sep. 30, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaborations

7.	Collaborations

Pfizer

Pursuant to an agreement entered 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). 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 equal to up to $17.5 million, payable upon the achievement of clinical, regulatory and commercial milestones. Following commercialization of any covered product, Pfizer would also receive a single-digit royalty on net product sales on a country-by-country basis for a predefined royalty term. No amounts have been paid to date under this new agreement.

ISU Abxis

On June 16, 2013, the Company signed a license and collaboration agreement with ISU Abxis, whereby the Company licensed its proprietary human Factor IX products to ISU Abxis for initial development in South Korea. Under the terms of the agreement, ISU Abxis is responsible for manufacturing, preclinical development activities and clinical development through completion of a proof-of-concept Phase 1/2 study in individuals with hemophilia B. The Company has the sole rights and responsibility for worldwide development, manufacture, and commercialization of Factor IX products after Phase 1/2 development. ISU Abxis may exercise its right of first refusal to acquire commercialization rights in South Korea, in which case they would be entitled to profit sharing on worldwide sales. ISU’s rights will also terminate if the Company enters into a license agreement with another party to develop, manufacture and commercialize Factor IX products in at least two major market territories.

ISU Abxis paid the Company an up-front signing fee of $1.75 million and is obligated to pay to the Company contingent milestone-based payments on the occurrence of certain defined development events, and reimbursement for a portion of the Company’s costs relating to intellectual property filings and maintenance thereof on products. The Company is obligated to pay ISU Abxis a percentage of all net profits it receives from collaboration products.

Contract revenue of $0.3 million and $0.1 million for the three months ended September 30, 2017 and 2016 and $0.7 million and $0.3 million for the nine months ended September 30, 2017 and 2016, respectively, reflected (i) for all periods presented the amortization of the up-front fee over the estimated period of the Company’s performance obligations under the agreement, which began in September 2013 when the agreement was executed and is estimated to conclude in February 2018 and (ii) $0.2 million and $0.5 for the three and nine months ended September 30, 2017, respectively, recorded for milestone payments, which are recognized over the estimated remaining period of the Company’s performance obligation under the agreement. During the nine months ended September 30, 2017, the Company received milestone payments from ISU Abxis of $0.9 million. The deferred revenue balance related to the ISU Abxis collaboration was $0.5 million and $0.3 million as of September 30, 2017 and December 31, 2016, respectively.

Net Loss per Share Attributable to Common Stockholders

9 Months Ended

Sep. 30, 2017

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 share attributable to common stockholders during the three and nine months ended September 30, 2017 and 2016 (in thousands, except share and per share data):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
Net loss attributable to common stockholders	$	(5,793	)	$	(4,771	)	$	(19,759	)	$	(13,195	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		4,310,561			789,796			3,043,919			771,713
Net loss available for common stockholders per share, basic and diluted	$	(1.34	)	$	(6.04	)	$	(6.49	)	$	(17.10	)

Since the Company was in a loss position for all periods presented, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders 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:

	September 30,		December 31,
	2017		2016
Options to purchase common stock		771,995		140,990
Convertible preferred stock⁽¹⁾		1,100,000		—
Common stock warrants		2,053,114		12,063
Redeemable convertible notes		39,814		140,743
Total		3,964,923		293,796

(1)

As of September 30, 2017, represents 5,500 shares of Series A Preferred Stock on an as converted basis to 1.1 million shares of common stock.

Stockholders’ Equity

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Stockholders' Equity

9.	Stockholders’ Equity

At the Market Issuance Sales Agreement — On March 16, 2016, the Company signed a Capital on Demand^TM Sales Agreement with JonesTrading Institutional Services LLC (“JonesTrading”). In accordance with the terms of the sales agreement, the Company was able to offer and sell shares of its common stock having a gross aggregate offering price up to $6.5 million, subject to certain limitations, from time to time in one or more public offerings of the Company’s common stock, with JonesTrading acting as agent, in transactions pursuant to a shelf registration statement that was declared effective by the SEC on April 28, 2016.

The Company sold an aggregate of 479,681 shares of common stock in the open market at a weighted-average selling price of $13.55 per share, for net proceeds (net of commissions) of $6.3 million through September 30, 2017, of which $5.5 million were sold in the nine months ended September 30, 2017, in the Capital on Demand^TM program. The Company charged approximately $0.2 million for JonesTrading commission against additional paid-in capital through September 30, 2017. As of September 30, 2017, the Company has no more common stock available for sale under the program.

April 2017 Underwritten Public Offering — On April 12, 2017, the Company issued and sold in a registered, underwritten public offering an aggregate of (i) 1,470,000 shares of common stock (including 540,000 shares of common stock sold pursuant to the exercise of the Underwriter’s overallotment option), (ii) 13,350 shares of Series A Preferred Stock, each convertible into 200 shares of common stock and (iii) warrants to purchase 2,070,000 shares of common stock at an exercise price of $5.50 per share (including 270,000 sold pursuant to the exercise of the Underwriter’s overallotment option). The net proceeds to the Company, after deducting the underwriting discounts and commissions and offering expenses payable by the Company were approximately $18.6 million.

Series A Convertible Preferred Stock — In connection with the closing on April 12, 2017 of the public offering, the Company filed the Certificate of Designation of Preferences, Rights and Limitations of the Series A Preferred Stock (the “Certificate of Designation”) with the Secretary of State of the State of Delaware. The Certificate of Designation describes the rights, preferences and privileges of the shares of Series A Preferred Stock. With certain exceptions, the shares of Series A Preferred Stock rank on par with the shares of the Common Stock, in each case, as to dividend rights and distributions of assets upon liquidation, dissolution or winding up of the Company.

Upon its issuance, the Series A Preferred Stock was not considered a liability or temporary equity and as such the Series A Preferred Stock was recorded in permanent equity on the Company’s balance sheet.

The Company determined that the contingent liquidated damages feature embedded in the Series A Preferred Stock meets the criteria of a derivative that requires bifurcation from the Series A Preferred Stock. This derivative had an immaterial value as of September 30, 2017.

During the nine months ended September 30, 2017, 7,850 shares of the Company’s Series A Preferred Stock were converted into 1,570,000 shares of common stock of the Company. As of September 30, 2017, there were 5,500 shares of Series A Preferred Stock issued and outstanding.

Beneficial Conversion Feature Series A Preferred Stock (deemed dividend) — Each share of Series A Preferred Stock is convertible into 200 shares of common stock, at any time, at the option of the holder. The net proceeds to the Company of $18.6 million were allocated to the common stock, Preferred A Stock and warrants (see below) based on a relative fair value basis. This resulted in $10.1 million being allocated to the Preferred A Stock and reflected on an effective conversion price of $3.80 per share. On April 12, 2017, the date of issuance of the Series A Preferred Stock, the publicly traded common stock price was $5.28 per share.

Based on the guidance in ASC 470-20-20, the Company determined that a beneficial conversion feature exists, as the effective conversion price for the shares of Series A Preferred Stock at issuance was less than the fair value of the common stock into which the shares of Series A Preferred Stock are convertible. The beneficial conversion feature calculated based on the intrinsic value as of the date of issuance was approximately $4.0 million. This amount was then accreted as a deemed dividend, which is a non-cash transaction. As the conversion rights were 100% effective at the time of issuance, the deemed dividend was immediately charged to accumulated deficit.

Warrants — In connection with the closing on April 12, 2017 of the public offering and the overallotment option, the Company issued warrants to purchase 2,070,000 shares of common stock at an exercise price of $5.50 per share. Upon their issuance, the common stock warrants were determined to be equity instruments under ASC 480 and ASC 815-40.

The following is a summary of warrant activity for the nine months ended September 30, 2017:

	Number of Shares
	Underlying Warrants			Exercise Price		Expiration
Outstanding — December 31, 2016		12,039		$	145.11
Issued		2,070,000		$	5.50	April 12, 2022
Exercised		(28,925	)	$	5.50
Outstanding — September 30, 2017		2,053,114

Commitments and Contingencies

9 Months Ended

Sep. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

10.	Commitments and Contingencies

Operating Leases

The Company leases office space for its corporate headquarters in South San Francisco, California. The lease will expire in February 2018.

Future minimum lease payments under all non-cancelable operating leases as of September 30, 2017, were as follows (in thousands):

	Minimum Lease Payments
2017		187
2018		125
Total future minimum lease payments		312

Manufacturing Agreements

On May 20, 2016, the Company entered into a development and manufacturing services agreement with CMC ICOS Biologics, Inc. (“CMC”), pursuant to which CMC will conduct manufacturing development and, upon successful development of the manufacturing process, manufacture the Company’s next-generation Factor VIIa variant marzeptacog alfa (activated) that the Company intends to use in its clinical trials. The Company has agreed to a total of $3.8 million in payments to CMC pursuant to the initial statement of work under the Agreement, subject to completion of applicable work stages. As of September 30, 2017, the Company’s remaining obligations to CMC were $0.7 million under the agreement.

Interest and Other Income

9 Months Ended

Sep. 30, 2017

Other Income And Expenses [Abstract]

Interest and Other Income

11. Interest and Other Income

The following table shows the detail of other income/(expense), net for the three and nine month periods ended September 30, 2017 and 2016 (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Gain on sale of assets	$	—	$	804	$	—	$	804
Change in derivative liability		—		99		—		1,036
Other Income, net		85		38		185		163
Total Other Income/(expense), net	$	85	$	941	$	185	$	2,003

As of September 30, 2017 and December 31, 2016, the fair value of the derivative liability associated with the Notes (see Note 5) was immaterial.

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events In October 2017 the Company announced a strategic research collaboration with Mosaic Biosciences, Inc. (“Mosaic”) to develop intravitreal anti-complement factor 3 (C3) products for the treatment of Dry AMD and other retinal diseases. According to the agreement the Company and Mosaic will co fund the research. Dr. Usman, our Chief Executive Officer and a member of our board of directors, and Mr. Lawlor, a member of our board of directors, are members of the board of directors of Mosaic. The transaction was reviewed by disinterested members of our board of directors and approved by our audit committee.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2017
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 U.S. 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, 2016 (“Annual Report”). The Company’s significant accounting policies are included in “Part II - Item 8 - Financial Statements and Supplementary Data - Note 2 – Summary of Significant Accounting Policies” in the Company’s Annual Report. There have been no significant changes to these accounting policies during the first nine months of 2017.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

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 September 30, 2017 and December 31, 2016 (in thousands):

	September 30, 2017
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	10,973	$	—	$	—	$	10,973
U.S. government agency securities⁽³⁾		14,981	$	—	$	—		14,981
Restricted cash (money market funds)⁽²⁾		5,727		—		—		5,727
Agency securities⁽³⁾		—		1,496		—		1,496
Total financial assets	$	31,681	$	1,496	$	—	$	33,177

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

(2)	$5.5 million of restricted cash in the Indenture serves as full collateral for the redeemable convertible notes and $0.1 million of restricted cash serves as collateral for the Company’s corporate credit card and deposit for its facility lease.

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

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	10,156	$	—	$	—	$	10,156
Restricted cash (money market funds)⁽²⁾		19,593		—		—		19,593
U.S. government agency securities⁽³⁾		6,800		—		—		6,800
Total financial assets	$	36,549	$	—	$	—	$	36,549

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

(2)	$19.4 million of restricted cash in the Indenture serves as full collateral for the redeemable convertible notes and $0.1 million of restricted cash serves as collateral for the Company’s corporate credit card and deposit for its facility lease.

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

Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2017

Investments All Other Investments [Abstract]

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

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

September 30, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	10,973	$	—	$	—		$	10,973
U.S. government agency securities		14,980		2		(1	)		14,981
Restricted cash (money market funds)		5,727		—		—			5,727
Agency securities		1,495		1		—			1,496
Total financial assets	$	33,175	$	3	$	(1	)	$	33,177
Classified as:
Cash and cash equivalents								$	10,973
Short-term investments									16,477
Restricted cash (money market funds)									5,727
								$	33,177

December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	10,156	$	—	$	—		$	10,156
Restricted cash (money market funds)		19,593		—		—			19,593
U.S. government agency securities		6,802		—		(2	)		6,800
Total financial assets	$	36,551	$	—	$	(2	)	$	36,549
Classified as:
Cash and cash equivalents								$	10,156
Restricted cash (money market funds)									19,593
Short-term investments									6,800
								$	36,549

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

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, 2016		140,990		$	127.56		3.93
Options granted		692,000		$	4.54
Options canceled		(141	)	$	41.91
Options forfeited		(60,854	)	$	165.77
Outstanding — September 30, 2017		771,995		$	14.30		9.37
Exercisable — September 30, 2017		106,953		$	64.96		7.10
Vested and expected to vest — September 30, 2017		771,995		$	14.30		9.37

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 nine months ended September 30, 2017 and 2016:

	Nine Months Ended September 30,
	2017			2016
Employee Stock Options:
Risk-free interest rate		2.02	%		1.41	%
Expected term (in years)		5.99			5.92
Dividend yield		—			—
Volatility		110.42	%		75.04	%
Weighted-average fair value of stock options granted	$	3.79		$	16.05

Summary of Stock-Based Compensation Recognized

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development	$	62	$	68	$	97	$	172
General and administrative		263		120		459		333
Total stock-based compensation	$	325	$	188	$	556	$	505

Net Loss per Share Attributable to Common Stockholders (Tables)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Basic and Diluted Net Loss Per Share Attributable to Common Stockholders

	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
Net loss attributable to common stockholders	$	(5,793	)	$	(4,771	)	$	(19,759	)	$	(13,195	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		4,310,561			789,796			3,043,919			771,713
Net loss available for common stockholders per share, basic and diluted	$	(1.34	)	$	(6.04	)	$	(6.49	)	$	(17.10	)

Anti-dilutive Security not Included In Diluted per Share Calculations

	September 30,		December 31,
	2017		2016
Options to purchase common stock		771,995		140,990
Convertible preferred stock⁽¹⁾		1,100,000		—
Common stock warrants		2,053,114		12,063
Redeemable convertible notes		39,814		140,743
Total		3,964,923		293,796

(1)

As of September 30, 2017, represents 5,500 shares of Series A Preferred Stock on an as converted basis to 1.1 million shares of common stock.

Stockholders’ Equity (Tables)

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Summary of Warrant Activity

The following is a summary of warrant activity for the nine months ended September 30, 2017:

	Number of Shares
	Underlying Warrants			Exercise Price		Expiration
Outstanding — December 31, 2016		12,039		$	145.11
Issued		2,070,000		$	5.50	April 12, 2022
Exercised		(28,925	)	$	5.50
Outstanding — September 30, 2017		2,053,114

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

+ References + Details

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments under All Non-cancelable Operating Leases

Future minimum lease payments under all non-cancelable operating leases as of September 30, 2017, were as follows (in thousands):

	Minimum Lease Payments
2017		187
2018		125
Total future minimum lease payments		312

Interest and Other Income (Tables)

9 Months Ended

Sep. 30, 2017

Other Income And Expenses [Abstract]

Detail of Other Income/(Expense), Net

The following table shows the detail of other income/(expense), net for the three and nine month periods ended September 30, 2017 and 2016 (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Gain on sale of assets	$	—	$	804	$	—	$	804
Change in derivative liability		—		99		—		1,036
Other Income, net		85		38		185		163
Total Other Income/(expense), net	$	85	$	941	$	185	$	2,003

As of September 30, 2017 and December 31, 2016, the fair value of the derivative liability associated with the Notes (see Note 5) was immaterial.

Nature of Operations - Additional Information (Detail)		9 Months Ended
Nature of Operations - Additional Information (Detail)	Feb. 10, 2017 shares	Sep. 30, 2017 Segment shares	Feb. 02, 2017 shares	Dec. 31, 2016 shares
Organization and Nature of Operations [Line Items]
Number of operating segment \| Segment		1
Common stock, shares outstanding		4,310,561		801,756
2017 Reverse Stock Split
Organization and Nature of Operations [Line Items]
Reverse stock split, description		On February 10, 2017, the Company effected a reverse stock split of its common stock at a ratio of 1-for-15 (“2017 Reverse Stock Split”). The 2017 Reverse Stock Split was approved by the Company’s stockholders at a special meeting of stockholders held on February 2, 2017. As a result of the 2017 Reverse Stock Split, each 15 pre-split shares of common stock outstanding were automatically combined into one new share of common stock, and the number of outstanding shares of common stock on the date of the split was reduced from approximately 13.0 million shares to approximately 868,000 shares.
Reverse stock split ratio	0.06667
Common stock, shares outstanding	868,000		13,000,000

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

Sep. 30, 2017

Dec. 31, 2016

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

Assets, fair value

$ 33,177

$ 36,549

Money Market Funds

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

Assets, fair value

^[1]

10,973

10,156

Restricted cash (money market funds)

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

Assets, fair value

5,727

^[2]

19,593

^[3]

U.S. Government Agency Securities

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

Assets, fair value

^[4]

14,981

6,800

Agency Securities

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

Assets, fair value

^[4]

1,496

Fair Value, Inputs, Level 1

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

Assets, fair value

31,681

36,549

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]

10,973

10,156

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

5,727

^[2]

19,593

^[3]

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

^[4]

14,981

$ 6,800

Fair Value, Inputs, Level 2

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

Assets, fair value

1,496

Fair Value, Inputs, Level 2 | Agency Securities

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

Assets, fair value

^[4]

$ 1,496

[1]	Included in cash and cash equivalents on accompanying condensed consolidated balance sheets.
[2]	$5.5 million of restricted cash in the Indenture serves as full collateral for the redeemable convertible notes and $0.1 million of restricted cash serves as collateral for the Company’s corporate credit card and deposit for its facility lease.
[3]	$19.4 million of restricted cash in the Indenture serves as full collateral for the redeemable convertible notes and $0.1 million of restricted cash serves as collateral for the Company’s corporate credit card and deposit for its facility lease.
[4]	Included in short-term investments on accompanying condensed consolidated balance sheets and are classified as available-for-sale securities.

Assets and Liabilities Measured at Fair Value (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Collateral for Redeemable Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash	$ 5.5	$ 19.4
Collateral for Corporate Credit Card and Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash	$ 0.1	$ 0.1

Cash Equivalents, Restricted Cash and Short-Term Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 33,175	$ 36,551
Gross Unrealized Gains	3
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	33,177	36,549
Money Market Funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,973	10,156
Estimated Fair Value	10,973	10,156
Money Market Funds \| Restricted cash (money market funds)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,727	19,593
Estimated Fair Value	5,727	19,593
U.S. Government Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,980	6,802
Gross Unrealized Gains	2
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	14,981	6,800
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	10,973	10,156
Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	16,477	$ 6,800
Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,495
Gross Unrealized Gains	1
Estimated Fair Value	$ 1,496

Financial Instruments - Additional Information (Detail)	9 Months Ended
Financial Instruments - Additional Information (Detail)	Sep. 30, 2017 USD ($)
Fair Value Disclosures [Abstract]
Significant realized gains or losses on available-for-sale securities	$ 0

Redeemable Convertible Notes - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) d $ / shares	Sep. 30, 2016 USD ($)	Aug. 19, 2015 USD ($)
Debt Instrument [Line Items]
Redeemable convertible notes, redeemed	$ 5,500,000		$ 5,500,000
Gain on extinguishment of redeemable convertible notes	$ 0		0	$ 92,000
Redeemable convertible notes, redeemed during period			$ 13,915,000	4,075,000
Convertible Notes
Debt Instrument [Line Items]
Convertible notes, total outstanding principal amount					$ 37,000,000
Redeemable convertible notes, conversion per share price \| $ / shares	$ 137.85		$ 137.85
Convertible notes, maturity date			Feb. 19, 2018
Convertible notes, maturity period			30 months
Redeemable convertible notes, threshold trading days \| d			10
Redeemable convertible notes, conversion feature			$ 1,500,000
Redeemable convertible notes, estimated fair value	$ 37,100,000		37,100,000
Redeemable convertible notes, debt discount	1,400,000		1,400,000
Redeemable convertible notes, interest expense	0	$ 0	0	$ 0
Redeemable convertible notes, redeemed	$ 31,200,000		31,200,000
Conversion of convertible notes in to common stock, value			300,000
Redeemable convertible notes, redeemed during period			$ 13,900,000
Convertible Notes \| After Reverse Stock Split
Debt Instrument [Line Items]
Redeemable convertible notes, conversion per share price \| $ / shares	$ 137.85		$ 137.85

Summary of Option Activity Under Company's Equity Incentive Plans (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance	140,990
Number of Shares Underlying Outstanding Options, Options granted	692,000
Number of Shares Underlying Outstanding Options, Options canceled	(141)
Number of Shares Underlying Outstanding Options, Options forfeited	(60,854)
Number of Shares Underlying Outstanding Options, Ending Balance	771,995	140,990
Number of Shares Underlying Outstanding Options, Exercisable — September 30, 2017	106,953
Number of Shares Underlying Outstanding Options, Vested and expected to vest — September 30, 2017	771,995
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance	$ 127.56
Weighted- Average Exercise Price, Options granted	4.54
Weighted- Average Exercise Price, Options canceled	41.91
Weighted- Average Exercise Price, Options forfeited	165.77
Weighted- Average Exercise Price, Ending Balance	14.30	$ 127.56
Weighted- Average Exercise Price, Exercisable — September 30, 2017	64.96
Weighted- Average Exercise Price, Vested and expected to vest — September 30, 2017	$ 14.30
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	9 years 4 months 13 days	3 years 11 months 4 days
Weighted-Average Remaining Contractual Term (Years), Exercisable — September 30, 2017	7 years 1 month 6 days
Weighted-Average Remaining Contractual Term (Years), Vested and expected to vest — September 30, 2017	9 years 4 months 13 days

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock available for future grant	404,632
Shares remaining outstanding	771,995
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of stock options	5 years 11 months 27 days	5 years 11 months 1 day
Unrecognized employee stock based compensation expense	$ 3.1
Unrecognized employee stock based compensation expense, period for recognition	3 years 1 month 7 days

Fair Values of Stock Options Estimated Using Black-Scholes Valuation Model (Detail) - Employee Stock Option - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Risk-free interest rate	2.02%	1.41%
Expected term (in years)	5 years 11 months 27 days	5 years 11 months 1 day
Dividend yield	0.00%	0.00%
Volatility	110.42%	75.04%
Weighted-average fair value of stock options granted	$ 3.79	$ 16.05

Summary of Stock-Based Compensation Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 325	$ 188	$ 556	$ 505
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	62	68	97	172
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 263	$ 120	$ 459	$ 333

Collaborations - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Jun. 16, 2013	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 08, 2016
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Contract revenue		$ 318,000	$ 109,000	$ 700,000	$ 328,000
Pfizer Inc \| Collaboration Agreement \| Maximum
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Contingent cash payments upon achievement of clinical, regulatory and commercial milestones							$ 17,500,000
ISU Abxis
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Contract revenue		300,000	$ 100,000	700,000	$ 300,000
Deferred revenue		500,000		500,000		$ 300,000
Milestone payments recognized over the estimated remaining period of performance obligation		$ 200,000		500,000
Milestone Payment Received				$ 900,000
ISU Abxis \| Up Front Payment
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Amount received for research and development process	$ 1,750,000

Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (5,793)	$ (4,771)	$ (19,759)	$ (13,195)
Weighted-average number of shares used in computing net loss per share, basic and diluted	4,310,561	789,796	3,043,919	771,713
Net loss available for common stockholders per share, basic and diluted	$ (1.34)	$ (6.04)	$ (6.49)	$ (17.10)

Anti-dilutive Security not Included In Diluted per Share Calculations (Detail) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	3,964,923	293,796
Options To Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	771,995	140,990
Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,100,000
Common Stock Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	2,053,114	12,063
Redeemable Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	39,814	140,743

Anti-dilutive Security not Included In Diluted per Share Calculations (Parenthetical) (Detail) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred stock, shares outstanding	5,500	0
Conversion of preferred stock to common stock	3,964,923	293,796
Series A Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred stock, shares outstanding	5,500
Conversion of preferred stock to common stock	1,100,000

Stockholders' Equity - Additional Information (Detail) - USD ($)		9 Months Ended		19 Months Ended
	Apr. 12, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016	Mar. 16, 2016
Stockholders Equity Disclosure [Line Items]
Common stock, value of shares issued under sales agreement		$ 4,000		$ 4,000	$ 1,000
Net proceeds from sale of common stock	$ 18,600,000	$ 5,336,000	$ 865,000
Warrants to purchase common stock	2,070,000
Warrants exercise price	$ 5.50				$ 145.11
Preferred stock, shares issued		5,500		5,500	0
Preferred stock, shares outstanding		5,500		5,500	0
Net proceeds allocated to common stock, preferred A stock and warrants		$ 18,563,000
Overallotment Option
Stockholders Equity Disclosure [Line Items]
Warrants to purchase common stock	270,000
Series A Preferred Stock
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	13,350
Conversion of each preferred stock to common stock	200
Number of shares converted		7,850
Preferred stock, shares issued		5,500		5,500
Preferred stock, shares outstanding		5,500		5,500
Net proceeds allocated to preferred stock		$ 10,100,000
Effective conversion price		$ 3.80		$ 3.80
Common stock price, per share	$ 5.28
Intrinsic value of preferred stock	$ 4,000,000
Effective percentage of conversion rights	100.00%
Common Stock
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	1,470,000	439,880
Conversion of preferred stock to common stock		1,570,000
Common Stock \| Overallotment Option
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	540,000
Capital on Demand Sales Agreement with Jones Trading Institutional Services LLC
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares				479,681
Common stock weighted average selling price				$ 13.55
Net proceeds from sale of common stock		$ 5,500,000		$ 6,300,000
Commission against additional paid-in capital				$ 200,000
Common stock available for sale		0		0
Capital on Demand Sales Agreement with Jones Trading Institutional Services LLC \| Maximum
Stockholders Equity Disclosure [Line Items]
Common stock, value of shares issued under sales agreement						$ 6,500,000

Summary of Warrant Activity (Detail) - $ / shares	9 Months Ended
Summary of Warrant Activity (Detail) - $ / shares	Sep. 30, 2017	Apr. 12, 2017	Dec. 31, 2016
Warrants And Rights Note Disclosure [Abstract]
Number of Shares Underlying Warrants, Outstanding	12,039
Number of Shares Underlying Warrants, Issued	2,070,000
Number of Shares Underlying Warrants, Exercised	(28,925)
Number of Shares Underlying Warrants, Outstanding	2,053,114
Warrants Outstanding, Exercise Price		$ 5.50	$ 145.11
Warrants Issued, Exercise Price	$ 5.50
Warrants Exercised, Exercise Price	$ 5.50
Warrants Issued, Expiration	Apr. 12, 2022

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	May 20, 2016
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	2018-02
CMC ICOS Biologics, Inc.
Commitments And Contingencies Disclosure [Line Items]
Contractual payment obligations	$ 0.7	$ 3.8

Schedule of Future Minimum Lease Payments under All Non-cancelable Operating Leases (Detail) $ in Thousands	Sep. 30, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2017	$ 187
2018	125
Total future minimum lease payments	$ 312

Detail of Other Income/(Expense), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Income And Expenses [Abstract]
Gain on sale of assets		$ 804		$ 804
Change in derivative liability		99		1,036
Other Income, net	$ 85	38	$ 185	163
Total Other Income/(expense), net	$ 85	$ 941	$ 185	$ 2,003