Derivative Instruments and Hedging Activities Schedule of Derivative Instruments in Statement of Financial Position (Details) (Interest Rate Swap, Designated as Hedging Instrument, USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value
Derivatives, net fair value	$ (19,930)	$ (21,015)
Other current liabilities
Derivatives, Fair Value
Derivative liability, fair value	(12,503)	(11,644)
Other long-term liabilities
Derivatives, Fair Value
Derivative liability, fair value	$ (7,427)	$ (9,371)