Unaudited Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement And Statement Of Comprehensive Income [Abstract]
Revenue	$ 57	$ 170	$ 249	$ 494
Operating expenses:
Research and development	23,923	13,572	42,302	26,484
General and administrative	5,984	5,774	10,169	9,346
Total operating expenses	29,907	19,346	52,471	35,830
Other operating income	6,120	3,820	11,569	10,640
Operating loss	(23,730)	(15,356)	(40,653)	(24,696)
Other (expense) income, net	(686)	(114)	(1,251)	3,147
Loss before income tax	(24,416)	(15,470)	(41,904)	(21,549)
Income tax benefit	0	191	0	136
Net loss	$ (24,416)	$ (15,279)	$ (41,904)	$ (21,413)
Loss per share:
Basic (in dollars per share)	$ (0.27)	$ (0.23)	$ (0.48)	$ (0.32)
Diluted (in dollars per share)	$ (0.27)	$ (0.23)	$ (0.48)	$ (0.32)
Weighted-average shares used to compute loss per share:
Basic (in shares)	90,650,854	67,231,900	86,755,983	67,224,799
Diluted (in shares)	90,650,854	67,231,900	86,755,983	67,224,799
Other comprehensive income (loss):
Change in foreign currency translation adjustment	$ 540	$ (52)	$ 1,215	$ (4,676)
Comprehensive loss	$ (23,876)	$ (15,331)	$ (40,689)	$ (26,089)