CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 48,875	$ 8,035	$ 123,351	$ 16,824
Operating expenses:
Research and development	54,814	30,086	151,361	74,521
General and administrative	16,961	10,619	53,549	29,126
Total operating expenses	71,775	40,705	204,910	103,647
Loss from operations	(22,900)	(32,670)	(81,559)	(86,823)
Other income (expense):
Interest income (expense), net	1,050	1,880	5,382	6,034
Other income	1	0	16	0
Total other income, net	1,051	1,880	5,398	6,034
Net loss	(21,849)	(30,790)	(76,161)	(80,789)
Foreign currency translation adjustment	0	(3)	0	(3)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ (21,849)	$ (30,793)	$ (76,161)	$ (80,792)
Net loss per share – basic and diluted (in dollars per share)	$ (0.29)	$ (0.45)	$ (1.03)	$ (1.18)
Weighted average common shares outstanding – basic and diluted (in shares)	74,523,319	68,360,051	73,817,194	68,315,074