Schedule of Components of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Current Provision (Benefit) - Federal	$ 58,695	$ 86,459	$ 64,256
Current Provision (Benefit) - State	5,989	7,638	4,727
Current Provision (Benefit) - Total	64,684	94,097	68,983
Deferred Provision (Benefit) - Federal	(52,333)	7,274	(546)
Deferred Provision (Benefit) - State	2,979	(5,071)	(1,777)
Deferred Provision (Benefit) - Total	(49,354)	2,203	(2,323)
Provision for Income Taxes	$ 15,330	$ 96,300	$ 66,660