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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net loss	$ (6,142)	$ (3,044)	$ (4,704)	$ (6,550)	$ (9,848)	$ (8,981)	$ (13,890)	$ (25,379)
Basic and diluted net loss per common share	$ (0.54)			$ (1.08)			$ (1.23)	$ (4.23)
Weighted-average common shares used to compute basic and diluted net loss per share	11,285			6,040			11,280	5,998