Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Feb. 28, 2015	Jan. 31, 2015	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2015
Convertible Preferred Stock [Line Items]
Number of convertible preferred stock converted to common stock							30,381,987
Preferred stock conversion rate							100.00%
Preferred stock, shares issued					0	0
Preferred stock, shares outstanding					0	0
Series C Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued	2,564,652	162,407	2,619,951
Issuance of convertible preferred stock	$ 15,000	$ 950
Stock price	$ 5.84	$ 5.84
Series C Convertible Preferred Stock | 2014 Convertible Promissory Notes
Convertible Preferred Stock [Line Items]
Stock issued convertible debt			1,739,405	1,739,405
Series C Convertible Preferred Stock | Itochu Corporation Agreement
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued			880,546
Issuance of convertible preferred stock			$ 5,200
Stock price			$ 5.84	$ 5.84
Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued					0	0
Preferred stock, shares outstanding					0	0