Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues	$ 0	$ 0	$ 25,000	$ 0
Operating expenses:
Research and development	40,374	20,630	110,974	55,531
General and administrative	17,979	5,259	44,379	14,738
Total operating expenses	58,353	25,889	155,353	70,269
Loss from operations	(58,353)	(25,889)	(130,353)	(70,269)
Other income (expense):
Interest and other income, net	2,174	1,475	5,368	2,778
Interest expense	(17)	(21)	(55)	(64)
Total other income (expense), net	2,157	1,454	5,313	2,714
Net loss	$ (56,196)	$ (24,435)	$ (125,040)	$ (67,555)
Net loss per share—basic and diluted (in dollars per share)	$ (1.28)	$ (0.65)	$ (3.12)	$ (1.95)
Weighted average common shares outstanding—basic and diluted (in shares)	43,803,508	37,654,324	40,041,321	34,623,773
Comprehensive loss:
Net loss	$ (56,196)	$ (24,435)	$ (125,040)	$ (67,555)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	(114)	0	61	0
Total other comprehensive income (loss)	(114)	0	61	0
Total comprehensive loss	$ (56,310)	$ (24,435)	$ (124,979)	$ (67,555)