Quarterly report pursuant to Section 13 or 15(d)

Debt (Details 2)

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Debt (Details 2) (USD $)
In Thousands
Jun. 30, 2011
Dec. 31, 2010
Carrying amount and estimated fair value of debt    
Debt, net $ 2,299,416 $ 2,323,681
Carrying Amount
   
Carrying amount and estimated fair value of debt    
Fixed-rate debt 1,455,739 1,559,034
Variable- rate debt 843,677 764,647
Debt, net 2,299,416 2,323,681
Total Estimated Fair Value
   
Carrying amount and estimated fair value of debt    
Fixed-rate debt 1,464,754 1,579,022
Variable- rate debt 849,935 769,247
Debt, net $ 2,314,689 $ 2,348,269