Income Taxes - Summary of Reconciliation Income Tax Provision from the Statutory Federal Income Tax Rate (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes at federal statutory rate (35%)	$ 16,643,000	$ 16,121,000	$ 15,947,000
State income taxes, net of federal benefit	1,973,000	1,704,000	1,535,000
Uncertain tax positions	88,000	78,000	1,346,000
Permanent items and tax credits	(705,000)	(100,000)	94,000
Adjustments to returns as filed	80,000	(232,000)	(1,978,000)
Other	(9,000)	(36,000)	30,000
Total	$ 18,070,000	$ 17,535,000	$ 16,974,000