Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Income tax (benefit) expense	$ (164,287,000)	$ (134,781,000)	$ (61,975,000)	$ 22,366,000	$ 166,048,000	$ 93,522,000	$ 117,976,000	$ 18,957,000	$ (338,677,000)	$ 396,503,000	$ 33,857,000
Deferred tax liabilities	777,947,000				1,113,081,000				777,947,000	1,113,081,000
Deductible limit	1,000,000								1,000,000
Net operating loss and credit carry forwards, state	32,700,000								32,700,000
Regular net operating loss carryforwards	620,600,000								620,600,000
Alternative minimum tax carryforwards	539,300,000								539,300,000
Deferred tax asset related to regular NOL	123,500,000								123,500,000
Accrued interest or penalties related to tax amounts	0								$ 0
Minimum
Income Taxes [Line Items]
Period during which net operating loss carryforwards and alternative minimum tax expire									Dec. 31, 2018
Maximum
Income Taxes [Line Items]
Period during which net operating loss carryforwards and alternative minimum tax expire									Dec. 31, 2035
Alternative Minimum Tax
Income Taxes [Line Items]
AMT credit carryforwards that are not subject to limitation or expiration	665,000								$ 665,000
Louisiana, Mississippi, Oklahoma and West Virginia
Income Taxes [Line Items]
Net operating loss and credit carry forwards, state	15,600,000								15,600,000
Pennsylvania
Income Taxes [Line Items]
Valuation allowance to net operating loss carryforward	16,000,000								16,000,000
Texas Margin
Income Taxes [Line Items]
Valuation allowance tax credit carryforward	1,000,000								1,000,000
Federal
Income Taxes [Line Items]
Valuation allowances	42,500,000				$ 0				42,500,000	$ 0
Deferred compensation plan
Income Taxes [Line Items]
Valuation allowances	$ 3,100,000								$ 3,100,000