Income Taxes - Summary of Income Tax Provision (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Current — Federal	$ 11,177,000	$ 16,456,000	$ 16,600,000
Current — State	1,905,000	2,834,000	2,591,000
Subtotal	13,082,000	19,290,000	19,191,000
Deferred — Federal	(955,000)	(1,508,000)	(1,679,000)
Deferred — State	81,000	288,000	23,000
Subtotal	(874,000)	(1,220,000)	(1,656,000)
Total	$ 12,208,000	$ 18,070,000	$ 17,535,000