Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 11,992	$ 9,737
Accrued compensation-related expenses	1,014	797
Accrued legal expenses	1,174	481
Accrued other expenses	367	963
Total accrued expenses	$ 14,547	$ 11,978