Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Balance, beginning of fiscal year	$ 49,066	$ 45,080	$ 41,769
Decrease related to prior year tax positions	(155)	(421)	(586)
Increases related to current year tax positions	6,563	4,407	3,897
Balance, end of fiscal year	$ 55,474	$ 49,066	$ 45,080