CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 60,209	$ 135,068	$ 205,825
Operating expenses:
Research and development	496,309	454,082	410,459
General and administrative	109,620	94,252	64,722
Total operating expenses	605,929	548,334	475,181
Loss from operations	(545,720)	(413,266)	(269,356)
Interest income	38,530	27,023	15,235
Other (expense) income, net	(7,526)	1,835	(1,875)
Loss before (benefit from) provision for income taxes	(514,716)	(384,408)	(255,996)
(Benefit from) provision for income taxes	(695)	326	(80)
Net loss	(514,021)	(384,734)	(255,916)
Reconciliation of net loss to net loss attributable to common stockholders:
Premium paid on repurchase of preferred stock	0	(4,127)	0
Cumulative preferred stock dividends	0	(12,996)	(13,925)
Net loss attributable to common stockholders	$ (514,021)	$ (401,857)	$ (269,841)
Net loss per share attributable to common stockholders, basic and diluted (usd per share)	$ (1.55)	$ (4.95)	$ (4.18)
Weighted average common shares used in net loss per share attributable to common stockholders, basic and diluted (in shares)	330,802,136	81,114,183	64,497,544
Collaboration revenue
Revenue:
Total revenue	$ 42,803	$ 76,519	$ 146,953
Collaboration revenue from related party (Note 14)
Revenue:
Total revenue	5,233	45,993	30,021
Grant revenue
Revenue:
Total revenue	$ 12,173	$ 12,556	$ 28,851