Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				6 Months Ended
	Feb. 15, 2018	Feb. 13, 2018	Apr. 12, 2017	Jun. 30, 2018	Jun. 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