Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 31, 2020
Payables and Accruals [Abstract]
Accrued R&D expenses	$ 19,294	$ 15,500
Accrued compensation-related expenses	13,016	9,309
Accrued commercial expenses	7,889	818
Accrued professional service fees	1,334	1,126
Accrued other expenses	2,844	2,307
Accrued expenses	$ 44,377	$ 29,060