Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Payables and Accruals [Abstract]
Accrued R&D expenses	$ 15,500	$ 46,947
Accrued compensation-related expenses	9,309	5,024
Accrued professional service fees	1,126	370
Accrued other expenses	3,125	1,394
Total accrued expenses	$ 29,060	$ 53,735