Long-term Debt and Derivatives (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011
Derivatives instruments impact on consolidated statement of income
Derivatives Not Designated as Hedging Instruments, Gain (Loss) Recognized in Income on Derivative	$ (1)	$ (4)
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	(1)	(4)
De-designated as hedging instruments
Derivatives instruments impact on consolidated statement of income
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	600	2,500
Derivatives in a Cash Flow Hedging Relationship
Derivatives instruments impact on consolidated statement of income
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(332)	(672)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(3,625)	(8,173)
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)	(332)	(672)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	$ (3,625)	$ (8,173)