Income Taxes - Schedule of Effective Tax Rates Vary from Federal Statutory Rates (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Earnings Before Income Taxes	$ 591,485	$ 617,937	$ 588,593
Income Taxes at Statutory Rate	124,212	129,766	123,605
State Income Taxes, net	14,680	18,172	16,821
Statutory Depletion in Excess of Cost	(9,927)	(9,883)	(8,253)
Excess Tax Benefit from Stock Compensation	(3,951)	(5,417)	(1,593)
Meals and Entertainment Disallowance	478	524	484
Limitation on Officers' Compensation	4,843	6,513	3,009
Valuation Allowance	500	500	(7,205)
Other	(2,766)	123	185
Provision for Income Taxes	$ 128,069	$ 140,298	$ 127,053
Effective Tax Rate	22.00%	23.00%	22.00%