Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total revenue	$ 6,868	$ 90,273
Type of Revenue [Extensible List]	us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember
Operating costs and expenses:
Cost of goods sold	$ 400
Research and development	368,815	$ 282,107	$ 210,277
Selling, general and administrative	345,777	201,404	62,878
Total operating costs and expenses	714,992	483,511	273,155
Loss from operations	(708,124)	(393,238)	(273,155)
Interest income, net	27,804	20,334	3,099
Other income (expense), net	82	22	(64)
Net loss	$ (680,238)	$ (372,882)	$ (270,120)
Net loss per share—basic and diluted	$ (13.38)	$ (8.08)	$ (7.09)
Weighted average number of common shares outstanding—basic and diluted	50,833,837	46,121,194	38,113,678
Comprehensive loss:
Net loss	$ (680,238)	$ (372,882)	$ (270,120)
Other comprehensive items:
Unrealized gain (loss) on marketable securities	1,810	(486)	73
Total other comprehensive gain (loss)	1,810	(486)	73
Total comprehensive loss	(678,428)	(373,368)	$ (270,047)
Product Revenue [Member]
Total revenue	3,957
Collaboration Revenue [Member]
Total revenue	$ 2,911	$ 90,273