Collaboration and License Agreements - Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Deferred Revenue
Deferred revenue, non-current	$ 397,369	$ 0
Cost Cash Advance from Collaboration Partner
Beginning balance	0
Additions	146,384
Imputed Interest	635
Deductions	(25,157)
Ending balance	121,862
Cost share advance from collaboration partner, current	92,415	0
Cost share advance from collaboration partner, non-current	29,447	$ 0
Collaboration expense to Pfizer
Deferred Revenue
Beginning balance	40,000
Additions	513,620
Imputed Interest	0
Deductions	(55,687)
Ending balance	497,933
Deferred revenue, current	100,600
Deferred revenue, non-current	$ 397,400