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Fair Value (Details) (USD $)
Jun. 30, 2011
Dec. 31, 2010
Fair Value (Details) [Abstract]    
Fair value of senior notes $ 298,500,000 $ 299,800,000
Carrying value of senior notes 300,000,000 300,000,000 [1]
Amount of difference between fair value and carrying value $ 1,500,000 $ 200,000
[1] Audited