Income Taxes - Reconciliation of Benefit from (Provision for) Income Taxes to Amount Computed by Applying Statutory Federal Income Tax Rate to (Loss) Income before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Provision Benefit For Income Taxes [Line Items]
Tax benefit (provision) at federal statutory rate	$ 22,149	$ (8,885)	$ (6,167)
State tax benefit (provision), net of federal benefit	2,605	(1,681)	(1,197)
Tax credits, net of valuation allowance	21,898	15,121	16,016
Non-deductible compensation	(2,852)	(2,659)	(2,457)
Non-deductible transaction costs		(645)	(30)
Non-deductible meals and entertainment	(727)	(794)	(751)
Stock-based compensation	799	(886)	(551)
Foreign effective tax rate differential, net of valuation allowance	(2,054)	(2,391)	(859)
Other	(1,031)	(380)	(185)
Total benefit from (provision for) income taxes	35,217	(3,617)	4,173
Federal [Member]
Provision Benefit For Income Taxes [Line Items]
Change in effective tax rate	(5,335)
State [Member]
Provision Benefit For Income Taxes [Line Items]
Change in effective tax rate	$ (235)	$ (417)	$ 354