Schedule of Components of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Items Giving Rise to Deferred Tax Liabilities - Excess Tax Depreciation and Amortization	$ (106,367)	$ (161,204)
Items Giving Rise to Deferred Tax Liabilities - Depletion	(11,069)	(18,638)
Items Giving Rise to Deferred Tax Liabilities - State Income Taxes, net	(14,265)	(11,455)
Items Giving Rise to Deferred Tax Liabilities - Other	(5,957)	(8,515)
Items Giving Rise to Deferred Tax Liabilities - Total Deferred Tax Liabilities	(137,658)	(199,812)
Items Giving Rise to Deferred Tax Assets - Change in Accruals	8,965	12,992
Items Giving Rise to Deferred Tax Assets - Inventory	4,276	1,242
Items Giving Rise to Deferred Tax Assets - Bad Debts	1,891	3,895
Items Giving Rise to Deferred Tax Assets - Long-term Incentive Compensation Plan	4,616	8,691
Items Giving Rise to Deferred Tax Assets - Credits and Other Carryforwards	12,879	13,103
Items Giving Rise to Deferred Tax Assets - Pension	1,108	4,178
Items Giving Rise to Deferred Tax Assets - Other		218
Items Giving Rise to Deferred Tax Assets - Subtotal	33,735	44,319
Items Giving Rise to Deferred Tax Assets - Valuation Allowance	(15,043)	(10,531)
Items Giving Rise to Deferred Tax Assets - Total Deferred Tax Assets	$ 18,692	$ 33,788