Selected Quarterly Financial Data (Unaudited) - Summary of Company's Quarterly Financial Information (Details) - 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]
Total revenues	$ 1,348	$ 939	$ 488	$ 1,262	$ 884	$ 984	$ 1,150	$ 1,347	$ 4,037	$ 4,365	$ 1,187
Loss from operations	(27,147)	(26,142)	(26,057)	(26,671)	(28,313)	(28,484)	(22,214)	(18,929)	(106,017)	(97,940)	(65,584)
Net loss	$ (27,167)	$ (26,073)	$ (25,868)	$ (26,206)	$ (27,704)	$ (27,548)	$ (21,172)	$ (18,009)	$ (105,314)	$ (94,433)	$ (64,775)
Net loss per share, basic and diluted	$ (0.69)	$ (0.69)	$ (0.69)	$ (0.71)	$ (0.77)	$ (0.77)	$ (0.63)	$ (0.62)	$ (2.79)	$ (2.81)	$ (7.26)