Summary of Principal Components of Net Deferred Income Tax Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Deferred income taxes	$ 0	$ 1,424
Deferred Tax Assets, Operating Loss Carryforwards	180,531	175,221
Total net deferred tax assets	8,266	81,906
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations	1,188	1,073
Deferred Tax Liabilities, Property, Plant and Equipment	7,728	83,330
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits	301	340
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	467	880
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	0	1,236
Deferred Tax Liabilities, ROU Obligations	538	0
Less: Valuation allowance	(179,006)	(114,939)
Deferred Tax Asset, Interest Carryforward	0	11,463
Deferred Tax Assets, Other	1,484	2,441
Deferred Tax Assets, ROU Assets	564	0
Deferred Tax Assets, Gross	187,272	196,845
Deferred Tax Assets, Derivative Instruments	2,737	4,191
Deferred Tax and Other Liabilities, Noncurrent	$ 8,266	$ 83,330

Deferred Tax Assets, ROU Assets

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Deferred Tax Liabilities, ROU Obligations

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences with jurisdictional netting.

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences, with jurisdictional netting, and liabilities classified as noncurrent and other.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible interest carryforward.

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

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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 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 allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible alternative minimum tax credit carryforwards.

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

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from asset retirement obligations. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset.

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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 property, plant, and equipment.

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