Income Taxes - Deferred Income Tax Assets (Liabilities) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Deferred tax assets related to uncertain tax positions	$ 8,000,000	$ 7,500,000
Deferred income tax assets:
Accrued liabilities	105,029,000	121,539,000
Retirement plans and postretirement benefits	38,004,000	24,312,000
Share-based compensation	16,261,000	20,468,000
Receivables and inventories	11,155,000	10,275,000
Derivative financial instruments	1,646,000	283,000
State net operating loss carryforwards	35,089,000	31,824,000
State tax credit carryforwards	4,748,000	3,007,000
Valuation allowances	(13,177,000)	(8,733,000)
Deferred income tax assets	198,755,000us-gaap_DeferredTaxAssetsNet	202,975,000us-gaap_DeferredTaxAssetsNet
Deferred income tax liabilities:
Property, plant and equipment	(209,168,000)	(199,004,000)
Intangible assets	(29,612,000)	(8,751,000)
Cancellation of debt	(11,299,000)	0
Other	(843,000)us-gaap_DeferredTaxLiabilitiesOther	(145,000)us-gaap_DeferredTaxLiabilitiesOther
Deferred income tax liabilities	(250,922,000)us-gaap_DeferredTaxLiabilities	(207,900,000)us-gaap_DeferredTaxLiabilities
Net deferred income tax asset (liability)	$ (52,167,000)us-gaap_DeferredTaxAssetsLiabilitiesNet	$ (4,925,000)us-gaap_DeferredTaxAssetsLiabilitiesNet

Deferred Tax Assets, Receivables and Inventories

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Deferred Tax Liabilities, Extinguishment of Debt

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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The tax effect as of the balance sheet date of the amount of future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance.

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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 liability attributable to taxable temporary differences from intangible assets including goodwill.

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Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed.

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