Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended					3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 22, 2016	Jan. 31, 2017	Sep. 30, 2016	Aug. 31, 2016	Aug. 31, 2015	Jul. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2013
Common Stock Warrants [Line Items]
(Gain) loss related to change in fair value									$ 6,739	$ 1,646
Fair value of warrants							$ 12,835		$ 12,835		$ 2,723
Common Stock Warrant
Common Stock Warrants [Line Items]
Warrants issued												128,231
Exercise price												$ 5.84
Common stock warrants, expiration date									Dec. 16, 2023
2015 Placement Common Stock Warrants | Insiders
Common Stock Warrants [Line Items]
Warrants issued					198,760	198,760
Exercise price					$ 5.00	$ 5.00
Common stock warrants, expiry term					5 years	5 years
2016 Placement Warrant
Common Stock Warrants [Line Items]
Warrants issued			1,380,745	1,380,745				1,380,745		1,380,745
Exercise price			$ 2.95	$ 2.95				$ 2.95		$ 2.95
Common stock warrants, expiry term			7 years	7 years
Proceed from private placement and equity issuances, gross			$ 13,800						$ 13,800
Fair value of warrants upon issuance under Private Placement	$ 2,700
Expected term (in years)	7 years								5 years 10 months 25 days		6 years 8 months 12 days
Expected volatility	61.60%								63.00%		63.60%
Risk-free interest rate	1.40%								2.00%		2.30%
Expected dividend yield	0.00%								0.00%		0.00%
(Gain) loss related to change in fair value							(1,000)	$ 1,600	$ 3,000	$ 1,600
Fair value of warrants							5,708		$ 5,708		$ 2,723
2017 Placement Warrants Liability
Common Stock Warrants [Line Items]
Warrants issued		1,720,512
Exercise price		$ 3.17
Proceed from private placement and equity issuances, gross		$ 26,100
Fair value of warrants upon issuance under Private Placement		$ 3,400
Expected term (in years)		7 years							6 years 3 months 19 days
Expected volatility		62.90%							63.80%
Risk-free interest rate		2.20%							2.10%
Expected dividend yield		0.00%							0.00%
(Gain) loss related to change in fair value							(1,300)		$ 3,700
Fair value of warrants							$ 7,127		$ 7,127
Warrant exercisable date		Jul. 31, 2017
Common stock warrants, expiry date		Jan. 31, 2024