Collaboration and License Agreements - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2021	Mar. 31, 2021
Deferred Revenue
Deferred revenue, current	$ 100,564	$ 100,564
Deferred revenue, non-current	426,021	397,369
Cost Cash Advance from Collaboration Partner
Beginning balance	121,862
Additions	0
Imputed Interest	1,210
Deductions	(38,304)
Ending balance	84,768
Cost share advance from collaboration partner, current	84,768	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	(71,348)
Ending balance	526,585
Deferred revenue, current	100,600	100,600
Deferred revenue, non-current	$ 426,000	$ 397,400