Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Feb. 28, 2015	Jan. 31, 2015	Dec. 31, 2017	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
Stock price	$ 5.84	$ 5.84
Issuance of convertible preferred stock	$ 15,000	$ 950
Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued			0	0	0
Preferred stock, shares outstanding			0	0	0