Convertible Preferred Stock - Summary of Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Preferred stock
Series A Noncumulative Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock		$ 30,908
Series B Noncumulative Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock		$ 31,074