Warrant Liabilities - Additional Information (Detail) - USD ($)		1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 05, 2015	Feb. 12, 2016	Jul. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Feb. 13, 2016	Apr. 30, 2015	Nov. 30, 2014
Class of Warrant or Right [Line Items]
Aggregate VWAP (percent)						1.00%
(Increase) decrease in the fair value of warrants liabilities				$ 130,000	$ 200,000	$ (29,000)	$ 1,295,000
Proceeds from issuance of common stock under tender offer						$ 10,000,000	70,000
Series A Warrants to Purchase Shares of Common Stock [Member] | IPO [Member]
Class of Warrant or Right [Line Items]
Number of common stock purchased upon issuance of warrants (in shares)				489,921		489,921
Exercise price of warrants exercised (in dollars per share)				$ 32.50		$ 32.50
Warrants term						5 years
Series A Warrant Liability [Member]
Class of Warrant or Right [Line Items]
Warrants exercised (in shares)				4,800		4,800
Warrants outstanding (in shares)				485,121		485,121
Warrant liability				$ 289,000	509,000	$ 289,000	509,000	$ 194,000
(Increase) decrease in the fair value of warrants liabilities				$ (126,000)	121,000	$ (95,000)	703,000
Series B Warrant Liability [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrants exercised (in dollars per share)	$ 32.50										$ 32.50
Warrants exercised (in shares)	117,902
Warrants outstanding (in shares)									0
Warrants cashless exercised (in shares)		20,460
Stock issued during period (in shares)		97,100
De-recognition of warrant liability	$ 6,700,000
Gross proceeds upon exercise of warrants	$ 3,800,000
Series B Warrant Liability [Member] | IPO [Member]
Class of Warrant or Right [Line Items]
Number of common stock purchased upon issuance of warrants (in shares)											489,921
Series C Warrant Liability [Member]
Class of Warrant or Right [Line Items]
Number of common stock purchased upon issuance of warrants (in shares)				118,083		118,083
Exercise price of warrants exercised (in dollars per share)	$ 31.25									$ 31.25
Warrant liability				$ 20,000	115,000	$ 20,000	115,000	$ 86,000
(Increase) decrease in the fair value of warrants liabilities				$ (4,000)	$ 79,000	$ (66,000)	$ 348,000
Warrants cashless exercised (in shares)			905
Proceeds from issuance of common stock under tender offer			$ 5,882
Series C Warrant Liability [Member] | Common Stock [Member]
Class of Warrant or Right [Line Items]
Issuance of shares upon cashless exercise warrants (in shares)			181