Income Taxes - Summary of Reconciliation Income Tax Provision from the Statutory Federal Income Tax Rate (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income taxes at federal statutory rate	$ 15,112,000	$ 16,643,000	$ 16,121,000
State income taxes, net of federal benefit	1,645,000	1,973,000	1,704,000
Uncertain tax positions	(464,000)	88,000	78,000
Permanent items and tax credits	(1,364,000)	(705,000)	(100,000)
Adjustments to returns as filed	138,000	80,000	(232,000)
Valuation allowance	236,000	0	0
Impact of tax reform	(3,095,000)	0	0
Other	0	(9,000)	(36,000)
Total	$ 12,208,000	$ 18,070,000	$ 17,535,000