Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Grant	$ 0	$ 3,888	$ 5,205
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 64,600	$ 36,719	$ 22,815
General and administrative	15,734	12,632	10,066
Total operating expenses	80,334	49,351	32,881
Loss from operations	(80,334)	(45,463)	(27,676)
Other income (expense):
Interest income	2,143	1,172	482
Other expense, net	(63)	(57)	(42)
Total other income	2,080	1,115	440
Net loss	$ (78,254)	$ (44,348)	$ (27,236)
Net loss per share, basic and diluted	$ (2.45)	$ (2.13)	$ (1.80)
Weighted-average common shares outstanding, basic and diluted	31,949,633	20,822,560	15,128,192