Convertible Preferred Stock - Summary of Convertible Preferred Stock (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	1,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series A Noncumulative Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	1,043,011
Preferred stock, shares issued	0	994,866
Preferred stock, shares outstanding	0	994,866
Preferred stock, liquidation value	$ 0	$ 31,000
Series B Noncumulative Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	5,133,477
Preferred stock, shares issued	0	2,151,722
Preferred stock, shares outstanding	0	2,151,722
Preferred stock, liquidation value	$ 0	$ 54,600