Summary of Significant Accounting Policies - Summary of Reconciliation of Denominator Used in Calculation of Basic and Diluted Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share Basic And Diluted [Abstract]
Net loss	$ (10,302)	$ (14,987)	$ (17,357)	$ (11,100)	$ (11,492)	$ (18,663)	$ (18,225)	$ (15,448)	$ (53,746)	$ (63,828)	$ (39,714)
Weighted-average common shares outstanding - basic									42,025	38,529	36,827
Weighted-average common shares outstanding - diluted									42,025	38,529	36,827
Net loss per common share, basic and diluted	$ (0.24)	$ (0.35)	$ (0.41)	$ (0.27)	$ (0.29)	$ (0.48)	$ (0.48)	$ (0.41)	$ (1.28)	$ (1.66)	$ (1.08)