Net Loss per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss	$ (36,487)	$ (41,538)	$ (43,875)	$ (41,569)	$ (78,025)	$ (85,444)
Net loss:	$ (36,487)	$ (41,538)	$ (43,875)	$ (41,569)	$ (78,025)	$ (85,444)
Denominator:
Weighted average common shares outstanding, basic and diluted	38,010		37,697		38,001	37,659
Net loss per share, basic and diluted	$ (0.96)		$ (1.16)		$ (2.05)	$ (2.27)