Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Payables and Accruals [Abstract]
Accrued R&D expenses	$ 25,988	$ 9,737
Accrued compensation-related expenses	2,792	797
Accrued legal expenses	439	481
Accrued other expenses	1,046	963
Total accrued expenses	$ 30,265	$ 11,978