Accumulated Other Comprehensive Income (Loss) (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reclassifications out of accumulated other comprehensive income (loss):
Interest expense	$ 18,708	$ 11,535	$ 37,430	$ 23,129
Income tax benefit	32,355	1,194	(4,044)	(2,562)
Net of tax in 2013	(66,060)	(90,805)	(3,947)	24,238
Total reclassifications	49	167	132	333
Amortization of loss on interest rate hedge | Amount Reclassified from Accumulated Other Comprehensive Income
Reclassifications out of accumulated other comprehensive income (loss):
Interest expense	(105)		(170)
Income tax benefit	41		67
Net of tax in 2013	(64)		(103)
Amortization of deferred actuarial loss and prior service cost | Amount Reclassified from Accumulated Other Comprehensive Income
Reclassifications out of accumulated other comprehensive income (loss):
Operating expenses	186	167	388	333
Income tax benefit	(73)		(153)
Net of tax in 2013	$ 113	$ 167	$ 235	$ 333