Income Taxes - Schedule of Components of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Income Tax Disclosure [Abstract]
Excess Tax Depreciation and Amortization	$ (271,694)	$ (256,999)
Depletable Assets	(4,532)	(4,455)
Investment in Joint Venture Basis Differences	(11,746)	(6,436)
Right-of-Use Assets	(7,699)	(7,996)
Inventory	0	(1,276)
Other	(3,679)	0
Total Deferred Tax Liabilities	(299,350)	(277,162)
Change in Accruals	7,902	12,866
Bad Debts	1,500	1,551
Long-Term Incentive Compensation Plan	5,898	4,609
Credits and Other Carryforwards	9,436	9,905
Lease Liability	9,475	9,303
Inventory	5,182	0
Pension	1,395	984
Other	0	1,002
Subtotal	40,788	40,220
Valuation Allowance	(4,100)	(3,000)
Total Deferred Tax Assets	36,688	37,220
Deferred Income Taxes, net	$ (262,662)	$ (239,942)

Deferred tax assets, lease liability.

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Deferred tax liabilities, depletable assets.

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Deferred tax liabilities, right of use asset.

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Amount of deferred tax liability attributable to taxable temporary differences.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from inventory.

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Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible tax credit carryforwards, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from pension benefits.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from provisions, reserves, allowances, and accruals, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from accrued liabilities.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary difference from allowance for credit loss on accounts receivable.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of deferred tax consequences attributable to taxable temporary differences derived from inventory.

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Amount of deferred tax liability attributable to taxable temporary differences from investments (excludes investments in subsidiaries and equity method investments).

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Amount of deferred tax liability attributable to taxable temporary differences classified as other.

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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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