Summary of Significant Accounting Policies Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other comprehensive income [Abstract]
Other Comprehensive Income (Loss), Change in Fair Value, Derivatives Qualifying as Hedges, before Tax	$ 0	$ 0	$ 26,904
Other Comprehensive Income (Loss), Change in Derivative Fair Value, Derivatives Qualifying as Hedges, Tax	0	0	(10,093)
Other Comprehensive Income (Loss), Change in Derivative Fair Value, Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	0	0	16,811
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Reclassification to Earnings, before Tax	(3,865)	20,707	10,608
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Reclassification to Earnings, Tax	1,601	(7,710)	(3,967)
Reclassification to earnings	(2,264)	12,997	6,641
Other Comprehensive Income (Loss), Minimum Pension Liability Net Adjustment, before Tax	(3,909)	(2,779)	(1,570)
Other Comprehensive Income (Loss), Minimum Pension Liability, Tax	(1,439)	(984)	(590)
Pension liability adjustment	$ (2,470)	$ (1,795)	$ (980)