Collaboration and License Agreements - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021
Milestone receivable from Pfizer
Beginning balance	$ 0
Additions	100,000
Imputed Interest	0
Deductions	0
Ending balance	100,000
Deferred Revenue
Deferred revenue, current	117,231	$ 100,564
Deferred revenue, non-current	451,193	397,369
Cost Cash Advance from Collaboration Partner
Beginning balance	121,862
Additions	0
Imputed Interest	601
Deductions	(18,285)
Ending balance	104,178
Cost share advance from collaboration partner, current	104,178	92,415
Cost share advance from Pfizer, non-current	0	29,447
Collaboration expense to Pfizer
Deferred Revenue
Beginning balance	497,933
Additions	100,000
Imputed Interest	0
Deductions	(29,509)
Ending balance	568,424
Deferred revenue, current	117,200	100,600
Deferred revenue, non-current	$ 451,200	$ 397,400