Income Taxes (Components of Income Tax Expense (Benefit)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract
CurrentFederalTaxExpenseBenefit	$ 26,637	$ 32,230		$ (27,926)
CurrentStateAndLocalTaxExpenseBenefit	0	0		(693)
Current Income Tax Expense (Benefit)	26,637	32,230		(28,619)
DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract
DeferredFederalIncomeTaxExpenseBenefit	196,997	(198,293)		148,362
DeferredStateAndLocalIncomeTaxExpenseBenefit	0	0		(237)
Deferred Income Tax Expense (Benefit)	196,997	(198,293)		148,125
Income Tax Expense (Benefit)	223,634	(166,063)	[1]	119,506	[1]
IncomeTaxEffectsAllocatedDirectlyToEquityAbstract
Other comprehensive income (loss)	(7,218)	(16,240)		25,591
AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation	5,730	0		0
IncomeTaxExpenseBenefitIntraperiodTaxAllocation	$ 222,146	$ (182,303)		$ 145,097

[1] “As previously reported” column represents balances reported in the Annual Report on Form 10-K for the year ended December 31, 2011, originally filed with the SEC on March 9, 2012. “As currently reported” column was included in the 8-K filed with the SEC on November 28, 2012.