Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 52,889	$ 54,873	$ 51,632	$ 45,770	$ 53,429	$ 53,292	$ 44,688	$ 33,400	$ 205,164	$ 184,809	$ 72,324
General and administrative	11,712	8,287	10,110	7,209	6,126	5,494	5,639	4,605	37,318	21,864	22,648
Total operating expenses	64,601	63,160	61,742	52,979	59,555	58,786	50,327	38,005	242,482	206,673	94,972
Loss from operations	(64,601)	(63,160)	(61,742)	(52,979)	(59,555)	(58,786)	(50,327)	(38,005)	(242,482)	(206,673)	(94,972)
Interest income	52	60	91	160	432	823	1,204	1,870
Other income	0	0	0	273	0	0	100	0	273	100	0
Net loss	$ (64,549)	$ (63,100)	$ (61,651)	$ (52,546)	$ (59,123)	$ (57,963)	$ (49,023)	$ (36,135)	$ (241,846)	$ (202,244)	$ (83,948)
Basic and diluted net loss per common share (in dollars per share)	$ (3.78)	$ (3.79)	$ (3.72)	$ (3.32)	$ (3.82)	$ (3.75)	$ (3.18)	$ (2.34)	$ (14.63)	$ (13.09)	$ (5.45)
Basic and diluted weighted average number of common shares outstanding	17,074,543	16,639,776	16,571,322	15,840,401	15,475,291	15,448,425	15,433,348	15,429,154	16,535,188	15,446,638	15,394,659