CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenues	$ 25,000	$ 0	$ 0
Operating expenses:
Research and development	157,610	82,887	39,514
Selling, general, and administrative	68,116	21,212	11,421
Total operating expenses	225,726	104,099	50,935
Loss from operations	(200,726)	(104,099)	(50,935)
Other income (expense):
Interest and other income, net	8,537	4,329	746
Interest expense	(67)	(84)	(95)
Total other income (expense), net	8,470	4,245	651
Net loss	$ (192,256)	$ (99,854)	$ (50,284)
Weighted average common shares outstanding—basic and diluted (in dollars per share)	$ (4.48)	$ (2.82)	$ (2.99)
Weighted average common shares outstanding—basic and diluted (in shares)	42,869,058	35,390,480	16,792,179
Comprehensive loss:
Net loss	$ (192,256)	$ (99,854)	$ (50,284)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	111	0	0
Total other comprehensive income (loss)	111	0	0
Total comprehensive loss	$ (192,145)	$ (99,854)	$ (50,284)