CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue:
Total revenue	$ 17,046	$ 41,757	$ 46,154	$ 99,647
Operating expenses:
Research and development	119,715	109,050	378,786	303,653
General and administrative	28,188	18,525	83,994	56,229
Total operating expenses	147,903	127,575	462,780	359,882
Loss from operations	(130,857)	(85,818)	(416,626)	(260,235)
Interest income	9,252	6,519	30,546	18,129
Other expense, net	(1,767)	(1,032)	(5,351)	(1,044)
Loss before income taxes	(123,372)	(80,331)	(391,431)	(243,150)
(Benefit from) provision for income taxes	(178)	0	(526)	158
Net loss	(123,194)	(80,331)	(390,905)	(243,308)
Net loss attributable to common stockholders (Note 11)	$ (123,194)	$ (87,819)	$ (390,905)	$ (257,758)
Net loss per share attributable to common stockholders, basic and diluted (usd per share)	$ (0.37)	$ (1.32)	$ (1.19)	$ (3.91)
Weighted average common shares used in net loss per share attributable to common stockholders, basic and diluted (in shares)	330,769,341	66,283,040	329,592,322	65,887,511
Collaboration revenue
Revenue:
Total revenue	$ 9,614	$ 16,935	$ 32,757	$ 56,530
Collaboration revenue from related party
Revenue:
Total revenue	3,724	19,727	4,726	33,166
Grant revenue
Revenue:
Total revenue	$ 3,708	$ 5,095	$ 8,671	$ 9,951