Subsequent Events - Additional Information (Detail) - USD ($)									12 Months Ended
	Mar. 15, 2018	Mar. 02, 2018	Feb. 19, 2018	Feb. 15, 2018	Feb. 13, 2018	Dec. 22, 2017	Dec. 20, 2017	Apr. 12, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 05, 2018	Feb. 21, 2018	Feb. 20, 2018	May 20, 2016
Subsequent Event [Line Items]
Common stock price, per share								$ 5.28
Net proceeds from sale of common stock						$ 9,700,000		$ 18,600,000		$ 5,336,000	$ 958,000
Redeemable convertible notes, outstanding balance										$ 5,085,000	$ 19,403,000
Preferred stock, shares outstanding										3,680	0
Number of warrants remaining										1,751,708	12,039
Proceeds received from warrants exercised										$ 1,817,000
Scenario Forecast
Subsequent Event [Line Items]
Proceeds received from warrants exercised									$ 9,300,000
AGC Biologics, Inc
Subsequent Event [Line Items]
Contractual obligation payments										$ 700,000					$ 3,800,000
Convertible Notes
Subsequent Event [Line Items]
Convertible notes, maturity date										Feb. 19, 2018
Common Stock
Subsequent Event [Line Items]
Firm commitment underwritten public offering shares							1,105,263
Issuance of stock, shares						1,105,263		1,470,000		439,880	39,743
Common stock price, per share						$ 9.50
Conversion of convertible securities, shares										1,934,000	8
Common Stock | Overallotment Option
Subsequent Event [Line Items]
Issuance of stock, shares								540,000
Subsequent Event
Subsequent Event [Line Items]
Net proceeds from sale of common stock				$ 106,700,000
Redeemable convertible notes, outstanding balance														$ 0
Preferred stock, shares outstanding	0
Remaining outstanding warrants called												254,628
Number of warrants remaining	45,628
Subsequent Event | AGC Biologics, Inc
Subsequent Event [Line Items]
Contractual obligation payments													$ 5,600,000
Subsequent Event | Convertible Notes
Subsequent Event [Line Items]
Convertible notes, maturity date			Feb. 19, 2018
Redeemable convertible notes, outstanding balance			$ 0
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Firm commitment underwritten public offering shares					2,941,176
Issuance of stock, shares				3,382,352
Common stock price, per share				$ 34.00
Preferred stock called for conversion		3,580
Conversion of convertible securities, shares	716,000
Subsequent Event | Common Stock | Overallotment Option
Subsequent Event [Line Items]
Issuance of stock, shares				441,176