Derivative Instruments and Hedging Activities (Details) (Other long-term liabilities [Member], Derivatives designated as hedging instruments [Member], Interest rate swaps [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Other long-term liabilities [Member] | Derivatives designated as hedging instruments [Member] | Interest rate swaps [Member]
Liability Derivatives
Fair value of Derivative liability	$ (9,039)	$ (6,666)