Net Loss per Common Stock - Schedule of Computation of Basic and Diluted Net Loss Per Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator
Net loss	$ (37,002)	$ (21,860)	$ (24,027)
Accretion for liquidation preference on preferred stock			(1,133)
Accretion for share issuance costs on preferred stock			(20)
Tax expense on preferred stock			(100)
Reversal of tax payable on preferred stock due to conversion of preferred stock			1,898
Extinguishment of remaining share issuance costs due to conversion of preferred stock			(439)
Total loss attributable to common stockholders	$ (37,002)	$ (21,860)	$ (23,821)
Denominator
Weighted average number of shares used to compute basic and diluted net loss per common stock	18,893,515	12,637,839	8,667,387
Net loss per common stock attributable to common stockholders - basic and diluted	$ (1.96)	$ (1.73)	$ (2.75)