Selected Quarterly Financial Data - Summary of Selected Unaudited Consolidated Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 200	$ 100							$ 300
Operating expenses	18,113	14,544	$ 16,449	$ 16,135	$ 25,019	$ 13,264	$ 15,207	$ 13,502	65,241	$ 66,992	$ 55,417
Net loss	$ (18,023)	$ (14,505)	$ (16,462)	$ (31,912)	$ (47,462)	$ (12,903)	$ (14,878)	$ (13,032)	$ (80,902)	$ (88,275)	$ (53,335)
Basic and diluted net loss per share	$ (1.63)	$ (1.39)	$ (1.58)	$ (3.14)	$ (7.88)	$ (6.91)	$ (7.97)	$ (7.00)	$ (7.70)	$ (30.30)	$ (30.16)