Schedule of Effective Tax Rates Vary from Federal Statutory Rates (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Earnings Before Income Taxes	$ 79,442	$ 105,072	$ 109,671	$ 129,927	$ 43,607	$ 56,157	$ 98,367	$ 57,564	$ 424,112	$ 255,695	$ 283,778
Income Taxes at Statutory Rate									89,063	53,998	59,690
Increases (Decreases) in Tax Resulting from - State Income Taxes, net									11,713	3,579	5,868
Increases (Decreases) in Tax Resulting from - Statutory Depletion in Excess of Cost									(5,263)	(3,078)	(3,834)
Increases (Decreases) in Tax Resulting from - Excess Tax Benefit from Stock Compensation									(3,229)	307	(651)
Increases (Decreases) in Tax Resulting from - Meals and Entertainment Disallowance									220	537	610
Increases (Decreases) in Tax Resulting from - Limitation on Officers' Compensation									1,503	1,018	1,434
Increase (Decreases in Tax Resulting from -Impact of CARES Act of 2020										(35,936)
Increases (Decreases) in Tax Resulting from - Credits									(400)	(2,150)	(940)
Increases (Decreases) in Tax Resulting from - Valuation Allowance									300	2,212	(2,100)
Increases (Decreases) in Tax Resulting from - Change in Reserves									(2,916)	4,200
Increases (Decreases) in Tax Resulting from - Other									(1,045)	(183)	195
Provision for Income Taxes									$ 89,946	$ 24,504	$ 60,272
Effective Tax Rate									21.00%	10.00%	21.00%