Accumulated Other Comprehensive Income (Loss) (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Amounts reclassified out of each component of accumulated other comprehensive income (loss)
Interest expense	$ (52,618)	$ (28,067)
Other income (loss)	105	(6,993)
Income (loss) before income tax expense	(115,483)	49,293
Income tax expense (benefit)	66,039	(8,677)
Net income (loss)	(49,444)	40,616
Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Amounts reclassified out of each component of accumulated other comprehensive income (loss)
Net income (loss)	4,039
Gains and losses on cash flow hedges | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Amounts reclassified out of each component of accumulated other comprehensive income (loss)
Income (loss) before income tax expense	(997)
Income tax expense (benefit)	381
Net income (loss)	(616)
Gains and losses on cash flow hedges | Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Interest rate swaps
Amounts reclassified out of each component of accumulated other comprehensive income (loss)
Interest expense	(997)
Amortization of pension and postretirement benefit plans | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Amounts reclassified out of each component of accumulated other comprehensive income (loss)
Prior service cost	373
Net actuarial loss	7,168
Income (loss) before income tax expense	7,541
Income tax expense (benefit)	(2,882)
Net income (loss)	4,659
Gains and losses on available-for-sale securities | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Amounts reclassified out of each component of accumulated other comprehensive income (loss)
Other income (loss)	(4)
Income (loss) before income tax expense	(4)
Net income (loss)	$ (4)