Income Taxes - Components of Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal - Current	$ 134us-gaap_CurrentFederalTaxExpenseBenefit	$ 475us-gaap_CurrentFederalTaxExpenseBenefit	$ 0us-gaap_CurrentFederalTaxExpenseBenefit
State - Current	0	0	7
Total current income tax expense	134us-gaap_CurrentIncomeTaxExpenseBenefit	475us-gaap_CurrentIncomeTaxExpenseBenefit	7us-gaap_CurrentIncomeTaxExpenseBenefit
Federal - Deferred	273,576	122,853	82,841
State - Deferred	33,881	11,730	9,638
Total deferred income tax expense	307,457us-gaap_DeferredIncomeTaxExpenseBenefit	134,583us-gaap_DeferredIncomeTaxExpenseBenefit	92,479us-gaap_DeferredIncomeTaxExpenseBenefit
Total income tax expense	$ 307,591us-gaap_IncomeTaxExpenseBenefit	$ 135,058us-gaap_IncomeTaxExpenseBenefit	$ 92,486us-gaap_IncomeTaxExpenseBenefit

Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

Amount of current state and local tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of deferred federal income tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of deferred state and local tax expense (benefit) pertaining to income (loss) from continuing operations.