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Fair Value Measurement (Carrying Values And Fair Values Of The Company's Financial Instruments) (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Carrying Amount [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Credit facility debt $ 1,553,230 $ 1,604,846
Senior notes 686,917 686,434
Debt instruments 2,240,147 2,291,280
Estimated Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Credit facility debt 1,522,982 1,550,960
Senior notes 771,750 761,250
Debt instruments $ 2,294,732 $ 2,312,210