Net Loss per Share of Common Stock - Summary of Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (6,550)	$ (49,788)	$ (25,379)	$ (116,107)
Weighted-average shares used to compute basic and diluted net loss per share	6,040	5,945	5,998	5,889
Basic and diluted net loss per common share	$ (1.08)	$ (8.37)	$ (4.23)	$ (19.72)