Long-term Debt and Derivatives (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Derivatives instruments impact on consolidated statement of income
Derivatives Not Designated as Hedging Instruments, Gain (Loss) Recognized in Income on Derivative	$ (10,000)	$ (60,000)
Interest rate swap contracts
Derivatives instruments impact on consolidated statement of income
Derivatives Not Designated as Hedging Instruments, Gain (Loss) Recognized in Income on Derivative	(10,000)	(60,000)
Unrealized losses within accumulated other comprehensive loss		9,400,000
Designated as hedging instruments
Derivatives instruments impact on consolidated statement of income
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	7,200,000	15,400,000
Derivatives in a Cash Flow Hedging Relationship
Derivatives instruments impact on consolidated statement of income
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(672,000)	(13,998,000)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(8,173,000)	(24,424,000)
Derivatives in a Cash Flow Hedging Relationship | Interest rate swap contracts
Derivatives instruments impact on consolidated statement of income
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(672,000)	(13,998,000)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	$ (8,173,000)	$ (24,424,000)