Summary of Significant Accounting Policies - Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in Accumulated OCI (loss) balances [Roll Forward]
Beginning Balance	$ (111,000)
Current period change	(12,000)	(41,000)	18,000
Ending Balance	(123,000)	(111,000)
Qualifying Hedges [Member]
Change in Accumulated OCI (loss) balances [Roll Forward]
Beginning Balance	(44,000)
Current period change	(1,000)
Ending Balance	(45,000)
Marketable Securities [Member]
Change in Accumulated OCI (loss) balances [Roll Forward]
Beginning Balance	3,000
Current period change	0
Ending Balance	3,000
Pension and Other Postretirement Benefit Plans [Member]
Change in Accumulated OCI (loss) balances [Roll Forward]
Beginning Balance	(70,000)
Current period change	(11,000)
Ending Balance	$ (81,000)