Long-term Debt and Derivatives (Details 5) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Derivatives instruments impact on consolidated balance sheets
Fair value of derivative liabilities	$ 4,645	$ 16,746
Derivatives Designated as Hedging Instruments
Derivatives instruments impact on consolidated balance sheets
Fair value of derivative liabilities	4,645	13,034
Derivatives Designated as Hedging Instruments | Interest rate swap contracts
Derivatives instruments impact on consolidated balance sheets
Fair value of derivative liabilities	4,645	13,034
Derivatives Not Designated as Hedging Instruments
Derivatives instruments impact on consolidated balance sheets
Fair value of derivative liabilities		3,712
Derivatives Not Designated as Hedging Instruments | Interest rate swap contracts
Derivatives instruments impact on consolidated balance sheets
Fair value of derivative liabilities		$ 3,712