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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Oct. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
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	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		11,942,729

Condensed Consolidated Balance Sheets - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 35,998,000	$ 14,472,000
Short-term investments	93,223,000	17,971,000
Restricted cash	50,000	5,333,000
Prepaid and other current assets	3,538,000	1,333,000
Total current assets	132,809,000	39,109,000
Other assets, noncurrent	352,000	128,000
Property and equipment, net	255,000	276,000
Total assets	133,416,000	39,513,000
Current liabilities:
Accounts payable	369,000	747,000
Accrued compensation	1,082,000	1,366,000
Other accrued liabilities	1,840,000	1,322,000
Deferred revenue		212,000
Deferred rent, current portion	13,000	7,000
Redeemable convertible notes	0	5,085,000
Total current liabilities	3,304,000	8,739,000
Deferred rent, noncurrent portion	161,000
Total liabilities	3,465,000	8,739,000
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized; 0 and 3,680 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively
Common stock, $0.001 par value, 100,000,000 shares authorized; 11,942,729 and 6,081,230 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	12,000	6,000
Additional paid-in capital	322,468,000	204,262,000
Accumulated other comprehensive loss	(24,000)
Accumulated deficit	(192,505,000)	(173,494,000)
Total stockholders’ equity	129,951,000	30,774,000
Total liabilities and stockholders’ equity	$ 133,416,000	$ 39,513,000

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
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	3,680
Preferred stock, shares outstanding	0	3,680
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	11,942,729	6,081,230
Common stock, shares outstanding	11,942,729	6,081,230

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Contract revenue		$ 318	$ 6	$ 700
Type of Revenue [Extensible List]	cbio:ContractMember	cbio:ContractMember	cbio:ContractMember	cbio:ContractMember
Operating expenses:
Research and development	$ 5,575	$ 3,805	$ 13,235	$ 9,286
General and administrative	2,770	2,391	8,909	7,407
Total operating expenses	8,345	6,196	22,144	16,693
Loss from operations	(8,345)	(5,878)	(22,138)	(15,993)
Interest and other income, net	651	85	2,920	185
Net loss	(7,694)	(5,793)	(19,218)	(15,808)
Deemed dividend for convertible preferred stock beneficial conversion feature				(3,951)
Net loss attributable to common stockholders	$ (7,694)	$ (5,793)	$ (19,218)	$ (19,759)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.64)	$ (1.34)	$ (1.75)	$ (6.49)
Shares used to compute net loss per share attributable to common stockholders, basic and diluted	11,942,729	4,310,561	10,967,750	3,043,919

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (7,694)	$ (5,793)	$ (19,218)	$ (15,808)
Other comprehensive income:
Unrealized (loss) gain on available-for-sale securities	(28)	4	(24)	5
Total comprehensive loss	$ (7,722)	$ (5,789)	$ (19,242)	$ (15,803)

- Definition

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

+ References + Details

Condensed Consolidated Statement of Stockholders Equity (Unaudited) - 9 months ended Sep. 30, 2018 - 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	1,866			1,866
Issuance of common stock for follow-on offering, net of issuance costs	106,762		$ 4	106,758
Issuance of common stock for follow-on offering, net of issuance costs, shares			3,382,352
Issuance of common stock upon exercise of warrants	9,545		$ 2	9,543
Issuance of common stock upon exercise of warrants, shares			1,735,419
Conversion of preferred stock to common stock, shares		(3,680)	736,000
Stock options exercised for common stock	$ 36			36
Stock options exercised for common stock, shares	7,707		7,707
Conversion of redeemable convertible notes to common stock, value	$ 3			3
Conversion of redeemable convertible notes to common stock, shares			21
Unrealized loss on available-for-sale securities	(24)				$ (24)
Net loss	(19,218)					(19,218)
Balance at Sep. 30, 2018	$ 129,951		$ 12	$ 322,468	$ (24)	$ (192,505)
Balance (in shares) at Sep. 30, 2018			11,942,729

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

9 Months Ended

Sep. 30, 2018

Sep. 30, 2017

Operating Activities

Net loss

$ (19,218)

$ (15,808)

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

Stock-based compensation expense

1,866

556

Depreciation and amortization

106

132

Loss on disposal of assets

116

Changes in operating assets and liabilities:

Prepaid and other current assets

(2,429)

Accounts payable

(378)

623

Accrued compensation and other accrued liabilities

234

614

Deferred rent

167

(29)

Deferred revenue

(6)

200

Net cash flows used in operating activities

(19,542)

(13,623)

Investing Activities

Proceeds from maturities of short-term investments

60,337

6,800

Purchase of short-term investments

(135,612)

(16,474)

Purchases of property and equipment

(201)

(3)

Net cash flows used in investing activities

(75,476)

(9,677)

Financing Activities

Payments for the redemption of redeemable convertible notes

(5,082)

(13,915)

Proceeds from issuance of common stock, net of issuance costs

106,762

5,336

Proceeds from issuance of preferred stock, common stock and warrants for follow-on offering, net of issuance costs

18,563

Proceeds from exercise of stock options

Proceeds from exercise of warrants

9,545

159

Net cash flow provided by financing activities

111,261

10,143

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

16,243

(13,157)

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

19,805

29,857

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

^[1]

36,048

16,700

Supplemental Disclosure of Non-Cash Investing and Financing Activities:

Deemed dividend for convertible preferred stock beneficial conversion feature

3,951

Adoption of ASC 606

207

Conversion of redeemable convertible notes to common stock

Unrealized (loss) gain on investments

$ (24)

$ 1

[1]	(a) The following table provides a reconciliation of cash and restricted cash to amounts reported within the condensed consolidated balance sheets: Cash and cash equivalents $35,998 $10,973 Restricted cash 50 5,727 Total cash and restricted cash $36,048 $16,700

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

Sep. 30, 2018

Dec. 31, 2017

Sep. 30, 2017

Dec. 31, 2016

Statement Of Cash Flows [Abstract]

Cash and cash equivalents

$ 35,998

$ 14,472

$ 10,973

Restricted cash

5,333

5,727

Total cash and restricted cash

$ 36,048

^[1]

$ 19,805

$ 16,700

^[1]

$ 29,857

[1]	(a) The following table provides a reconciliation of cash and restricted cash to amounts reported within the condensed consolidated balance sheets: Cash and cash equivalents $35,998 $10,973 Restricted cash 50 5,727 Total cash and restricted cash $36,048 $16,700

Nature of Operations

9 Months Ended

Sep. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Operations

1.	Nature of Operations

Catalyst Biosciences, Inc. and its subsidiary (the “Company” or “Catalyst”) is a clinical-stage 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”).

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 September 30, 2018 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, 2018

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, 2017 (“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. As discussed in our Annual Report, the Company adopted the new revenue standards in the first quarter of 2018, using the modified retrospective method through a cumulative adjustment to equity. There have been no other significant changes to these accounting policies during the first nine months of 2018.

Effective January 1, 2018, the Company adopted Accounting Standards Codification (“ASC”) 606 using the modified retrospective method through a cumulative adjustment to equity, which resulted in an immaterial $0.2 million decrease to our opening balance of accumulated deficit as of January 1, 2018. The Company enters into collaboration arrangements that may include the receipt of payments for up-front license fees, success-based milestone payments, full time equivalent based payments for research services, product supplies, and royalties on any future sales of commercialized products that result from the collaborations.

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

Accounting Pronouncements Recently Adopted

In November 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-18, Restricted Cash, which requires amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. The Company adopted ASU 2016-18 effective January 1, 2018, using a retrospective transition method to each period presented. The adoption of this ASU changed previously reported amounts in the condensed consolidated statement of cash flows for the nine months ended September 30, 2017, by decreasing the Company’s cash flows provided by financing activities by $13.9 million as compared to previously reported amounts for the prior year period.

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

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

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

Adopting ASU No. 2014-09, Revenue from Contracts with Customers, or the new revenue standard, involved new estimates and judgments related to the estimates of stand-alone selling prices and the allocation of discounts and variable consideration in allocating the transaction price. The Company recognized revenue earlier under the current new standard and may have more variability due to significant estimates involved under the new accounting guidance.

Accounting Pronouncements Not Yet Adopted

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which replaces the existing guidance for leases. The new standard establishes a right-of-use (“ROU”) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. In July 2018, the FASB issued ASU No. 2018-11, which provides entities with an additional transition method to adopt Topic 842. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. Using the new transition method, the Company initially applies the new lease standard at the adoption date, versus at the beginning of the earliest period presented, and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption.

The Company expects to elect this transition method at the adoption date of January 1, 2019. The Company continues to assess the effect the guidance will have on its existing accounting policies and the Consolidated Financial Statements, and expects there will be an increase in assets and liabilities on the Consolidated Balance Sheets at adoption due to the recording of right-of-use assets and corresponding lease liabilities, which is expected to be material. Refer to Note 10 — Commitments and Contingencies for information about the Company’s lease obligations.

Fair Value Measurements

9 Months Ended

Sep. 30, 2018

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, 2018.

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 1, 2 or 3 during the periods presented. As of September 30, 2018 there was no derivative liability and as of December 31, 2017 the fair value of the derivative liability was immaterial.

The following tables present the fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 (in thousands):

	September 30, 2018
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	22,213	$	—	$	—	$	22,213
U.S. government agency securities⁽²⁾		93,223		—		—		93,223
Agency securities⁽¹⁾		—		13,648				13,648
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	115,486	$	13,648	$	—	$	129,134

(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, 2017
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	14,334	$	—	$	—	$	14,334
U.S. government agency securities⁽³⁾		16,471		—		—		16,471
Restricted cash (money market funds)⁽²⁾		5,333		—		—		5,333
Agency securities⁽³⁾		—		1,500		—		1,500
Total financial assets	$	36,138	$	1,500	$	—	$	37,638

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

(2)	$5.2 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, 2018

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, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	22,213	$	—	$	—		$	22,213
U.S. government agency securities		93,246				(23	)		93,223
Agency securities		13,649		—		(1	)		13,648
Restricted cash (money market funds)		50		—		—			50
Total financial assets	$	129,158	$	—	$	(24	)	$	129,134
Classified as:
Cash and cash equivalents								$	35,861
Short-term investments									93,223
Restricted cash (money market funds)									50
								$	129,134

December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	14,334	$	—	$	—		$	14,334
U.S. government agency securities		16,474		—		(3	)		16,471
Restricted cash (money market funds)		5,330		3		—			5,333
Agency securities		1,500		—		—			1,500
Total financial assets	$	37,638	$	3	$	(3	)	$	37,638
Classified as:
Cash and cash equivalents								$	14,334
Short-term investments									17,971
Restricted cash (money market funds)									5,333
								$	37,638

There have been no material 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, 2018

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, which matured on February 19, 2018. The Notes did not bear interest. The principal amount of the Notes were 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. On February 19, 2018, the Notes matured, and the remaining Notes were repaid in full with cash from the restricted cash indenture and an immaterial amount were converted to common stock. The Company has no outstanding Notes remaining as of September 30, 2018.

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 were the Company’s secured obligation, and the Indenture did not limit its other indebtedness, secured or unsecured.

The conversion to common stock feature of the Notes was determined to be a derivative liability requiring bifurcation and separate accounting. 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 were being recorded within interest and other income in the consolidated statements of operations. The Company remeasured the derivative liability to fair value until the earlier of the conversion, redemption or maturity of the redeemable convertible notes.

As of September 30, 2018, there was no derivative liability and as of December 31, 2017, 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.

Stock Based Compensation

9 Months Ended

Sep. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Based Compensation

6.	Stock Based Compensation

2018 Omnibus Incentive Plan

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

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

	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)
Outstanding — December 31, 2017		821,741		$	13.69		9.17
Options granted		564,050		$	13.43
Options exercised		(7,707	)	$	4.63
Options expired		(15,667	)	$	158.94
Options canceled/forfeited		(43,315	)	$	7.76
Outstanding — September 30, 2018		1,319,102		$	12.10		8.92
Exercisable — September 30, 2018		344,273		$	19.48		8.06

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 5.97 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, 2018 and 2017:

	Nine Months Ended September 30,
	2018			2017
Employee Stock Options:
Risk-free interest rate		2.66	%		2.02	%
Expected term (in years)		5.97			5.99
Dividend yield		—			—
Volatility		93.60	%		110.42	%
Weighted-average fair value of stock options granted	$	10.28		$	3.79

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Research and development	$	161	$	62	$	413	$	97
General and administrative⁽¹⁾		541		263		1,445		459
Total stock-based compensation	$	702	$	325	$	1,858	$	556

(1)

2018 includes $0.1 million in modification stock-based compensation expense related to a Board member’s departure.

As of September 30, 2018, 1,349,818 shares of common stock were available for future grant and 1,319,102 options to purchase shares of common stock were outstanding. As of September 30, 2018, the Company had unrecognized employee stock-based compensation expense of $6.9 million, related to unvested stock awards, which is expected to be recognized over an estimated weighted-average period of 2.91 years.

2018 Employee Stock Purchase Plan

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

A total of 120,000 shares of common stock may be granted in accordance with the terms of the ESPP. As of September 30, 2018, no shares of common stock have been issued to employees participating in the ESPP and 120,000 shares are available for issuance under the ESPP. Compensation expense, representing the discount to the quoted market price, for the ESPP was immaterial as of September 30, 2018.

Collaborations	9 Months Ended
Collaborations	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations	7. Collaborations ISU Abxis On September 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 right 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 Abxis’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 the United States, European Union or Asia, subject to ISU Abxis’s retained rights in South Korea. 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 if ISU Abxis makes an optional milestone payment to Catalyst. Contract revenue of $0 and $0.3 million for the three months ended September 30, 2018 and 2017 and $0 and $0.7 million for the nine months ended September 30, 2018 and 2017, respectively, reflects (i) the amortization of the up-front fee over the estimated period of our performance obligations, which concluded in February 2018, and (ii) milestone payments received from ISU Abxis, which were recognized through February 2018, the estimated remaining period of the Company’s performance obligation under the agreement, of which the Company received $0 and $0.9 million for the nine months ended September 30, 2018 and 2017, respectively. The adoption of the new revenue standards resulted in a $0.2 million cumulative adjustment to the Company’s opening balance of accumulated deficit as of January 1, 2018. The deferred revenue balance related to the ISU Abxis collaboration was $0 and $0.2 million as of September 30, 2018 and December 31, 2017, respectively.

Net Loss per Share Attributable to Common Stockholders

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Loss per Share Attributable to Common Stockholders

8.	Net Loss per Share Attributable to Common Stockholders

The following table sets forth the computation of the basic and diluted net loss per common share during the three- and nine-months ended September 30, 2018 and 2017 (in thousands, except share and per share data):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Net loss attributable to common stockholders	$	(7,694	)	$	(5,793	)	$	(19,218	)	$	(19,759	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		11,942,729			4,310,561			10,967,750			3,043,919
Net loss available for common stockholders per share, basic and diluted	$	(0.64	)	$	(1.34	)	$	(1.75	)	$	(6.49	)

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:

	Nine Months Ended September 30,
	2018		2017
Options to purchase common stock		1,319,102		771,995
Convertible preferred stock⁽¹⁾		—		1,100,000
Common stock warrants		12,039		2,053,114
Redeemable convertible notes		—		39,814
Total		1,331,141		3,964,923

(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, 2018

Equity [Abstract]

Stockholders' Equity

9.	Stockholders’ Equity

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.

During the nine months ended September 30, 2018 and 2017, 3,680 and 7,850 shares of the Company’s Series A Preferred Stock were converted into 736,000 and 1,570,000 shares of common stock of the Company. As of September 30, 2018, there were no shares of Series A Preferred Stock issued and outstanding.

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 net proceeds allocated to the warrants on a relative fair value basis resulted in $5.0 million being allocated to the warrants. As of September 30, 2018, the Company has no warrants outstanding associated with this offering.

The following is a summary of warrant activity for the nine months ended September 30, 2018:

	Number of Shares			Weighted Average
	Underlying Warrants			Exercise Price
Outstanding — December 31, 2017		1,751,708		$	6.46
Exercised		(1,735,419	)	$	5.50
Forfeited		(4,250	)	$	5.50
Outstanding —September 30, 2018		12,039		$	145.11

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

9 Months Ended

Sep. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

10.	Commitments and Contingencies

Pfizer

Pursuant to the termination 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 engineered Factor VIIa, 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 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. During the nine months ended September 30, 2018, the Company paid Pfizer a $1 million milestone payment based on the dosing of the first patient in the ongoing Phase 2 study, recorded as a R&D expense.

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 and, together with AGC the Company has successfully manufactured MarzAA for the Phase 2 portion of a planned Phase 2/3 clinical trial. The Company has agreed to a total of $3.8 million in payments to AGC pursuant to the initial statement of work under the Agreement, subject to completion of applicable work stages. As of September 30, 2018, the Company has $0.3 million in payment obligations to AGC remaining under the initial statement of work for MarzAA and $0.3 million in accrued liabilities.

On February 21, 2018, the Company and AGC entered into a new statement of work under the development and manufacturing services agreement dated May 20, 2016, between the Company and AGC. Under the new statement of work, the Company has engaged AGC for the process transfer and commercial scale cGMP manufacturing of Dalcinonacog alfa (“DalcA”) (formerly CB 2679d/ISU304), Catalyst’s next-generation engineered coagulation Factor IX being developed for the treatment of severe hemophilia B. The Company has agreed to a total of approximately $5.6 million in payments pursuant to the new statement of work, including the commercial scale manufacturing of DalcA, subject to completion of applicable work stages. As of September 30, 2018, the Company has $3.9 million in payment obligations to AGC remaining under the initial statement of work for DalcA.

Operating Leases

The Company leases office and research space under operating leases that expired in February 2018. In November 2017, the Company entered into a new office lease agreement to lease approximately 8,606 rentable square feet of space located in South San Francisco, California. The term of the lease is five years and two months, starting February 16, 2018. The Company relocated its corporate headquarters into this new space in February 2018. On August 10, 2018, the Company entered into an amendment to the existing office lease agreement to lease an additional approximately 4,626 rentable square feet and will be coterminous with the original lease term above.

Future minimum annual lease payments under all non-cancelable operating leases as of September 30, 2018, were as follows (in thousands):

	Minimum Lease Payments
Remaining in 2018	$	122
2019		563
2020		580
2021		598
2022		616
2023		209
Total future minimum lease payments	$	2,688

Related Parties	9 Months Ended
Related Parties	Sep. 30, 2018
Related Party Transactions [Abstract]
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 (C3) products for the treatment of dry age-related macular degeneration (“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, the chairman of our board of directors, are also members of the board of directors of Mosaic. Expenses related to the collaboration were $0.5 million and $0 for the three months ended September 30, 2018 and 2017 and $0.9 million and $0 for the nine months ended September 30, 2018 and 2017, respectively.

Interest and Other Income

9 Months Ended

Sep. 30, 2018

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 nine-month periods ended September 30, 2018 and 2017 (in thousands):

	Three Months Ended September 30,					Nine Months Ended September 30,
	2018			2017		2018			2017
Interest income	$	652		$	85	$	1,539		$	185
Loss on disposal of property and equipment		—			—		(116	)		—
Other income, net		(1	)		—		1,497			—
Total interest and other income, net	$	651		$	85	$	2,920		$	185

Total other income of $1.5 million for the nine months ended September 30, 2018, reflects milestone payments received under an agreement associated with neuronal nicotinic receptor (“NNR”) assets sold in 2016.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2018
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, 2017 (“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. As discussed in our Annual Report, the Company adopted the new revenue standards in the first quarter of 2018, using the modified retrospective method through a cumulative adjustment to equity. There have been no other significant changes to these accounting policies during the first nine months of 2018. Effective January 1, 2018, the Company adopted Accounting Standards Codification (“ASC”) 606 using the modified retrospective method through a cumulative adjustment to equity, which resulted in an immaterial $0.2 million decrease to our opening balance of accumulated deficit as of January 1, 2018. The Company enters into collaboration arrangements that may include the receipt of payments for up-front license fees, success-based milestone payments, full time equivalent based payments for research services, product supplies, and royalties on any future sales of commercialized products that result from the collaborations. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when the Company satisfies each performance obligation.
Accounting Pronouncements Recently Adopted	Accounting Pronouncements Recently Adopted In November 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-18, Restricted Cash, which requires amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. The Company adopted ASU 2016-18 effective January 1, 2018, using a retrospective transition method to each period presented. The adoption of this ASU changed previously reported amounts in the condensed consolidated statement of cash flows for the nine months ended September 30, 2017, by decreasing the Company’s cash flows provided by financing activities by $13.9 million as compared to previously reported amounts for the prior year period. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The standard provides guidance on how certain cash receipts and payments are presented and classified in the statement of cash flows. The standard is intended to reduce current diversity in practice. The Company adopted ASU 2016-15 effective January 1, 2018, and this guidance did not have an impact on the Company’s financial statements. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Topic 825-10), which updates certain aspects of recognition, measurement, presentation and disclosure of financial instruments. Subsequently, in February 2018, the FASB issued ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall (Topic 825-10), which clarifies certain aspects of ASU 2016-01, which includes provisions to accounting for equity investments, financial liabilities under the fair value option and presentation and disclosure requirements for financial instruments. The amended guidance requires equity securities, except for those accounted for under the equity method of accounting, with determinable fair values to be measured at fair value with changes in fair value recognized in net income (loss). The Company adopted ASU 2016-01 and 2018-03 effective January 1, 2018, and this guidance did not have a material impact on the Company’s financial statements, as the Company only has debt securities. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which amends the existing accounting standards for revenue recognition. ASU 2014-09 is based on principles that govern the recognition of revenue at an amount an entity expects to be entitled when products are transferred to customers. Subsequently, the FASB has issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; and ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, (collectively, the “new revenue standards”). The Company adopted the new revenue standards effective January 1, 2018, using the modified retrospective method through a cumulative adjustment to equity. The Company has identified that the most significant change relates to its accounting for collaboration arrangements with multiple deliverables, in particular, the ISU Abxis agreement. Under the old guidance, such deliverables and consideration must be accounted for under a single unit of accounting along with other arrangement deliverables and consideration that does not have stand-alone value and are recognized as revenue over the estimated period that the performance obligations are to be performed. Under the current new standard however, the total arrangement consideration is allocated to each performance obligation based on its estimated stand-alone selling price and revenue is recognized as each performance obligation is satisfied. As a result, revenue for this transaction is recorded in an earlier period than under the old guidance, resulting in a $0.2 million increase to the Company’s opening balance of accumulated deficit as of January 1, 2018. Adopting ASU No. 2014-09, Revenue from Contracts with Customers, or the new revenue standard, involved new estimates and judgments related to the estimates of stand-alone selling prices and the allocation of discounts and variable consideration in allocating the transaction price. The Company recognized revenue earlier under the current new standard and may have more variability due to significant estimates involved under the new accounting guidance.
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which replaces the existing guidance for leases. The new standard establishes a right-of-use (“ROU”) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. In July 2018, the FASB issued ASU No. 2018-11, which provides entities with an additional transition method to adopt Topic 842. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. Using the new transition method, the Company initially applies the new lease standard at the adoption date, versus at the beginning of the earliest period presented, and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The Company expects to elect this transition method at the adoption date of January 1, 2019. The Company continues to assess the effect the guidance will have on its existing accounting policies and the Consolidated Financial Statements, and expects there will be an increase in assets and liabilities on the Consolidated Balance Sheets at adoption due to the recording of right-of-use assets and corresponding lease liabilities, which is expected to be material. Refer to Note 10 — Commitments and Contingencies for information about the Company’s lease obligations.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

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, 2018 and December 31, 2017 (in thousands):

	September 30, 2018
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	22,213	$	—	$	—	$	22,213
U.S. government agency securities⁽²⁾		93,223		—		—		93,223
Agency securities⁽¹⁾		—		13,648				13,648
Restricted cash (money market funds)		50		—		—		50
Total financial assets	$	115,486	$	13,648	$	—	$	129,134

(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, 2017
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds⁽¹⁾	$	14,334	$	—	$	—	$	14,334
U.S. government agency securities⁽³⁾		16,471		—		—		16,471
Restricted cash (money market funds)⁽²⁾		5,333		—		—		5,333
Agency securities⁽³⁾		—		1,500		—		1,500
Total financial assets	$	36,138	$	1,500	$	—	$	37,638

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

(2)	$5.2 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, 2018

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, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	22,213	$	—	$	—		$	22,213
U.S. government agency securities		93,246				(23	)		93,223
Agency securities		13,649		—		(1	)		13,648
Restricted cash (money market funds)		50		—		—			50
Total financial assets	$	129,158	$	—	$	(24	)	$	129,134
Classified as:
Cash and cash equivalents								$	35,861
Short-term investments									93,223
Restricted cash (money market funds)									50
								$	129,134

December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	14,334	$	—	$	—		$	14,334
U.S. government agency securities		16,474		—		(3	)		16,471
Restricted cash (money market funds)		5,330		3		—			5,333
Agency securities		1,500		—		—			1,500
Total financial assets	$	37,638	$	3	$	(3	)	$	37,638
Classified as:
Cash and cash equivalents								$	14,334
Short-term investments									17,971
Restricted cash (money market funds)									5,333
								$	37,638

Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

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, 2017		821,741		$	13.69		9.17
Options granted		564,050		$	13.43
Options exercised		(7,707	)	$	4.63
Options expired		(15,667	)	$	158.94
Options canceled/forfeited		(43,315	)	$	7.76
Outstanding — September 30, 2018		1,319,102		$	12.10		8.92
Exercisable — September 30, 2018		344,273		$	19.48		8.06

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, 2018 and 2017:

	Nine Months Ended September 30,
	2018			2017
Employee Stock Options:
Risk-free interest rate		2.66	%		2.02	%
Expected term (in years)		5.97			5.99
Dividend yield		—			—
Volatility		93.60	%		110.42	%
Weighted-average fair value of stock options granted	$	10.28		$	3.79

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,
	2018		2017		2018		2017
Research and development	$	161	$	62	$	413	$	97
General and administrative⁽¹⁾		541		263		1,445		459
Total stock-based compensation	$	702	$	325	$	1,858	$	556

(1)

2018 includes $0.1 million in modification stock-based compensation expense related to a Board member’s departure.

Net Loss per Share Attributable to Common Stockholders (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Basic and Diluted Net Loss Per Common Share

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Net loss attributable to common stockholders	$	(7,694	)	$	(5,793	)	$	(19,218	)	$	(19,759	)
Weighted-average number of shares used in computing net loss per share, basic and diluted		11,942,729			4,310,561			10,967,750			3,043,919
Net loss available for common stockholders per share, basic and diluted	$	(0.64	)	$	(1.34	)	$	(1.75	)	$	(6.49	)

Anti-dilutive Security not Included In Diluted per Share Calculations

	Nine Months Ended September 30,
	2018		2017
Options to purchase common stock		1,319,102		771,995
Convertible preferred stock⁽¹⁾		—		1,100,000
Common stock warrants		12,039		2,053,114
Redeemable convertible notes		—		39,814
Total		1,331,141		3,964,923

(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, 2018

Equity [Abstract]

Summary of Warrant Activity

The following is a summary of warrant activity for the nine months ended September 30, 2018:

	Number of Shares			Weighted Average
	Underlying Warrants			Exercise Price
Outstanding — December 31, 2017		1,751,708		$	6.46
Exercised		(1,735,419	)	$	5.50
Forfeited		(4,250	)	$	5.50
Outstanding —September 30, 2018		12,039		$	145.11

- 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, 2018

Commitments And Contingencies Disclosure [Abstract]

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

Future minimum annual lease payments under all non-cancelable operating leases as of September 30, 2018, were as follows (in thousands):

	Minimum Lease Payments
Remaining in 2018	$	122
2019		563
2020		580
2021		598
2022		616
2023		209
Total future minimum lease payments	$	2,688

Interest and Other Income (Tables)

9 Months Ended

Sep. 30, 2018

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 nine-month periods ended September 30, 2018 and 2017 (in thousands):

	Three Months Ended September 30,					Nine Months Ended September 30,
	2018			2017		2018			2017
Interest income	$	652		$	85	$	1,539		$	185
Loss on disposal of property and equipment		—			—		(116	)		—
Other income, net		(1	)		—		1,497			—
Total interest and other income, net	$	651		$	85	$	2,920		$	185

Nature of Operations - Additional Information (Detail)	9 Months Ended
Nature of Operations - Additional Information (Detail)	Sep. 30, 2018 Segment
Accounting Policies [Abstract]
Number of operating segment	1

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Cumulative adjustment to accumulated deficit				$ 207
Decrease in cash flows from financing activities as compared to previously reported amounts	$ (111,261)	$ (10,143)
Accumulated Deficit
Summary Of Significant Accounting Policies [Line Items]
Cumulative adjustment to accumulated deficit				$ 207
ASU 2014-09 \| ISU Abxis \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Accumulated Deficit
Summary Of Significant Accounting Policies [Line Items]
Cumulative adjustment to accumulated deficit			$ 200
ASU 2016-18
Summary Of Significant Accounting Policies [Line Items]
Decrease in cash flows from financing activities as compared to previously reported amounts	$ 13,900

Fair Value Measurements - Additional Information (Detail)	Sep. 30, 2018 USD ($)
Fair Value Disclosures [Abstract]
Derivative liability	$ 0

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

Sep. 30, 2018

Dec. 31, 2017

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

Assets, fair value

$ 129,134

$ 37,638

Money Market Funds

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

Assets, fair value

^[1]

22,213

14,334

Restricted cash (money market funds)

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

Assets, fair value

5,333

^[2]

U.S. Government Agency Securities

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

Assets, fair value

^[3]

93,223

16,471

Agency Securities

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

Assets, fair value

13,648

^[1]

1,500

^[3]

Fair Value, Inputs, Level 1

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

Assets, fair value

115,486

36,138

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]

22,213

14,334

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

5,333

^[2]

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

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

Assets, fair value

^[3]

93,223

16,471

Fair Value, Inputs, Level 2

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

Assets, fair value

13,648

1,500

Fair Value, Inputs, Level 2 | Agency Securities

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

Assets, fair value

$ 13,648

^[1]

$ 1,500

^[3]

[1]	Included in cash and cash equivalents on accompanying condensed consolidated balance sheets.
[2]	$5.2 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.

Assets and Liabilities Measured at Fair Value (Parenthetical) (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Collateral for Redeemable Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash	$ 5.2
Collateral for Corporate Credit Card and Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash	$ 0.1

Cash Equivalents, Restricted Cash and Short-Term Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 129,158	$ 37,638
Gross Unrealized Gains		3
Gross Unrealized Losses	(24)	(3)
Estimated Fair Value	129,134	37,638
Money Market Funds \| Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,213	14,334
Estimated Fair Value	22,213	14,334
Money Market Funds \| Restricted cash (money market funds)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50	5,330
Gross Unrealized Gains		3
Estimated Fair Value	50	5,333
U.S. Government Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	93,246	16,474
Gross Unrealized Losses	(23)	(3)
Estimated Fair Value	93,223	16,471
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	35,861	14,334
Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	93,223	17,971
Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,649	1,500
Gross Unrealized Losses	(1)
Estimated Fair Value	$ 13,648	$ 1,500

Financial Instruments - Additional Information (Detail)	9 Months Ended
Financial Instruments - Additional Information (Detail)	Sep. 30, 2018 USD ($)
Fair Value Disclosures [Abstract]
Material realized gains or losses on available-for-sale securities	$ 0

Redeemable Convertible Notes - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Aug. 19, 2015
Debt Instrument [Line Items]
Redeemable convertible notes, outstanding balance	$ 0	$ 5,085,000
Derivative liability	$ 0
Convertible Notes
Debt Instrument [Line Items]
Convertible notes, total outstanding principal amount			$ 37,000,000
Convertible notes, maturity date	Feb. 19, 2018
Derivative liability	$ 0
Convertible Notes \| After Reverse Stock Split
Debt Instrument [Line Items]
Redeemable convertible notes, conversion per share price	$ 137.85

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Millions		9 Months Ended
	Jun. 13, 2018	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted		564,050
Number of common stock available for future grant		1,349,818
Shares remaining outstanding		1,319,102
2018 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	1,500,000
2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock available for future grant		120,000
Maximum employee subscription rate	15.00%
Number of common stock authorized for issuance		120,000
Number of common stock stock issued		0
2018 Employee Stock Purchase Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of fair market value of common stock	85.00%
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of stock options		5 years 11 months 19 days	5 years 11 months 26 days
Unrecognized employee stock based compensation expense		$ 6.9
Unrecognized employee stock based compensation expense, period for recognition		2 years 10 months 28 days

Summary of Option Activity Under Company's Equity Incentive Plans (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance	821,741
Number of Shares Underlying Outstanding Options, Options granted	564,050
Number of Shares Underlying Outstanding Options, Options exercised	(7,707)
Number of Shares Underlying Outstanding Options, Options expired	(15,667)
Number of Shares Underlying Outstanding Options, Options canceled/forfeited	(43,315)
Number of Shares Underlying Outstanding Options, Ending Balance	1,319,102	821,741
Number of Shares Underlying Outstanding Options, Exercisable - June 30, 2018	344,273
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance	$ 13.69
Weighted- Average Exercise Price, Options granted	13.43
Weighted- Average Exercise Price, Options exercised	4.63
Weighted- Average Exercise Price, Options expired	158.94
Weighted- Average Exercise Price, Options Canceled/forfeited	7.76
Weighted- Average Exercise Price, Ending Balance	12.10	$ 13.69
Weighted- Average Exercise Price, Exercisable - June 30, 2018	$ 19.48
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	8 years 11 months 1 day	9 years 2 months 1 day
Weighted-Average Remaining Contractual Term (Years), Exercisable - June 30, 2018	8 years 21 days

Fair Values of Stock Options Estimated Using Black-Scholes Valuation Model (Detail) - Employee Stock Option - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Risk-free interest rate	2.66%	2.02%
Expected term (in years)	5 years 11 months 19 days	5 years 11 months 26 days
Dividend yield	0.00%	0.00%
Volatility	93.60%	110.42%
Weighted-average fair value of stock options granted	$ 10.28	$ 3.79

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

3 Months Ended

9 Months Ended

Sep. 30, 2018

Sep. 30, 2017

Sep. 30, 2018

Sep. 30, 2017

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

Total stock-based compensation

$ 702

$ 325

$ 1,858

$ 556

Research and development

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

Total stock-based compensation

161

413

General and Administrative

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

Total stock-based compensation

^[1]

$ 541

$ 263

$ 1,445

$ 459

[1]	2018 includes $0.1 million in modification stock-based compensation expense related to a Board member’s departure.

Summary of Stock-Based Compensation Recognized (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 702	$ 325	$ 1,858	$ 556
Board Member’s Departure
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense			$ 100

Collaborations - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Sep. 16, 2013	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Contract revenue			$ 318	$ 6	$ 700
Cumulative adjustment to accumulated deficit		$ (192,505)		(192,505)			$ (173,494)
ISU Abxis
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Contract revenue		0	$ 300	0	700
Deferred revenue		$ 0		0			$ 200
Milestone Payment Received				$ 0	$ 900
ISU Abxis \| Difference between Revenue Guidance in Effect before and after Topic 606 \| ASU 2014-09
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Cumulative adjustment to accumulated deficit						$ 200
ISU Abxis \| Up Front Payment
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Amount received for research and development process	$ 1,750

Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (7,694)	$ (5,793)	$ (19,218)	$ (19,759)
Weighted-average number of shares used in computing net loss per share, basic and diluted	11,942,729	4,310,561	10,967,750	3,043,919
Net loss available for common stockholders per share, basic and diluted	$ (0.64)	$ (1.34)	$ (1.75)	$ (6.49)

Anti-dilutive Security not Included In Diluted per Share Calculations (Detail) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,331,141	3,964,923
Options To Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities	1,319,102	771,995
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	12,039	2,053,114
Redeemable Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti dilutive securities		39,814

Anti-dilutive Security not Included In Diluted per Share Calculations (Parenthetical) (Detail) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred stock, shares outstanding	0		3,680
Conversion of preferred stock to common stock	1,331,141	3,964,923
Series A Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred stock, shares outstanding	0	5,500
Conversion of preferred stock to common stock		1,100,000

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				9 Months Ended
	Feb. 15, 2018	Feb. 13, 2018	Apr. 12, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Stockholders Equity Disclosure [Line Items]
Warrants to purchase common stock			2,070,000
Warrants exercise price			$ 5.50	$ 145.11		$ 6.46
Net proceeds from sale of common stock	$ 106,800		$ 18,600	$ 106,762	$ 5,336
Preferred stock, shares issued				0		3,680
Preferred stock, shares outstanding				0		3,680
Proceeds allocated to warrants, net			$ 5,000
Number of warrants outstanding				12,039		1,751,708
Overallotment Option
Stockholders Equity Disclosure [Line Items]
Warrants to purchase common stock			270,000
April 2017 Underwritten Public Offering
Stockholders Equity Disclosure [Line Items]
Number of warrants outstanding				0
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				3,680	7,850
Preferred stock, shares issued				0
Preferred stock, shares outstanding				0	5,500
Common Stock
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	3,382,352		1,470,000
Conversion of preferred stock to common stock				736,000	1,570,000
Firm commitment underwritten public offering shares		2,941,176
Common stock price, per share	$ 34.00
Common Stock \| Overallotment Option
Stockholders Equity Disclosure [Line Items]
Issuance of stock, shares	441,176		540,000

Summary of Warrant Activity (Detail)	9 Months Ended
Summary of Warrant Activity (Detail)	Sep. 30, 2018 $ / shares shares
Warrants And Rights Note Disclosure [Abstract]
Number of Shares Underlying Warrants, Outstanding \| shares	1,751,708
Number of Shares Underlying Warrants, Exercised \| shares	(1,735,419)
Number of Shares Underlying Warrants, Forfeited \| shares	(4,250)
Number of Shares Underlying Warrants, Outstanding \| shares	12,039
Warrants Outstanding, Weighted Average Exercise Price \| $ / shares	$ 6.46
Warrants Exercised, Weighted Average Exercise Price \| $ / shares	5.50
Warrants Forfeited, Weighted Average Exercise Price \| $ / shares	5.50
Warrants Outstanding, Weighted Average Exercise Price \| $ / shares	$ 145.11

Commitments and Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018 USD ($) ft²	Aug. 10, 2018 ft²	Dec. 08, 2016 USD ($)	May 20, 2016 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	2018-02
South San Francisco, California \| New Office Lease Agreement
Commitments And Contingencies Disclosure [Line Items]
Leased area \| ft²	8,606
Operating lease term of contract	5 years 2 months
Operating lease commencement date	Feb. 16, 2018
South San Francisco, California \| Office Lease Agreement
Commitments And Contingencies Disclosure [Line Items]
Leased area \| ft²		4,626
Pfizer Inc \| Collaboration Agreement
Commitments And Contingencies Disclosure [Line Items]
Milestone payment	$ 1,000,000
Pfizer Inc \| Collaboration Agreement \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments upon achievement of clinical, regulatory and commercial milestones			$ 17,500,000
AGC Biologics, Inc \| MarzAA
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments	300,000			$ 3,800,000
Accrued liabilities	300,000
AGC Biologics, Inc \| Dalcinonacog alfa (“DalcA”)
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments	$ 3,900,000			$ 5,600,000

Schedule of Future Minimum Annual Lease Payments under All Non-cancelable Operating Leases (Detail) $ in Thousands	Sep. 30, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Remaining in 2018	$ 122
2019	563
2020	580
2021	598
2022	616
2023	209
Total future minimum lease payments	$ 2,688

Related Parties - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Mosaic \| Strategic Research Collaboration to Develop Intravitreal Anti-Complement Factor 3 (C3) Products
Related Party Transaction [Line Items]
Expenses related to collaboration	$ 0.5	$ 0.0	$ 0.9	$ 0.0

Detail of Interest and Other Income/(Expense), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income And Expenses [Abstract]
Interest income	$ 652	$ 85	$ 1,539	$ 185
Loss on disposal of property and equipment			(116)
Other income, net	(1)		1,497
Total interest and other income, net	$ 651	$ 85	$ 2,920	$ 185

Interest and Other Income - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Other Income And Expenses [Abstract]
Total other income reflects milestone payments received	$ (1)	$ 1,497