Summary of Significant Accounting Policies - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss allocated to common stock-basic and diluted	$ (11,421)	$ (10,726)	$ (13,088)	$ (26,282)	$ (24,038)	$ (23,075)	$ (35,235)	$ (73,395)
Denominator:
Weighted average number of common stock shares outstanding - basic and diluted	68,887,092			68,701,043			68,884,894	66,454,750
Net loss per share - basic and diluted:	$ (0.17)			$ (0.38)			$ (0.51)	$ (1.10)