Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Consolidated Statements of Operations [Abstract]
Revenue	$ 0	$ 0	$ 0
Operating expenses:
Research and development	106,382	58,623	53,270
General and administrative	27,921	17,528	17,886
Total operating expenses	134,303	76,151	71,156
Loss from operations	(134,303)	(76,151)	(71,156)
Research and development incentives	0	250	186
Interest expense	(6,967)	(5,958)	(6,039)
Interest and other income net	2,150	3,414	1,690
(Amortization of premium) accretion of discount on investments - net	(580)	1,175	801
Net loss	$ (139,700)	$ (77,270)	$ (74,518)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (2.52)	$ (1.58)	$ (1.89)
Weighted-average common shares outstanding - basic and diluted (in shares)	55,380,740	49,010,358	39,377,666