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, 2019	Mar. 31, 2018	Mar. 31, 2017
Provision Benefit For Income Taxes [Line Items]
Tax benefit (provision) at federal statutory rate	$ 23,201	$ 22,149	$ (8,885)
State tax benefit (provision), net of federal benefit	1,815	2,605	(1,681)
Tax credits, net of valuation allowance	26,836	21,898	15,121
Non-deductible compensation	(4,527)	(2,852)	(2,659)
Non-deductible transaction costs	(70)		(645)
Non-deductible meals and entertainment	(929)	(727)	(794)
Stock-based compensation	180	799	(886)
Foreign effective tax rate differential, net of valuation allowance	(1,552)	(2,054)	(2,391)
Unremitted subsidiary gains	(1,388)	(864)	162
Other	(1,868)	(167)	(542)
Total benefit from (provision for) income taxes	41,014	35,217	(3,617)
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	$ (684)	$ (235)	$ (417)