Quarterly report pursuant to Section 13 or 15(d)

Debt, Net (Details 2)

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Debt, Net (Details 2) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Carrying amount and estimated fair value of debt    
Carrying Value $ 2,130,170 $ 1,920,057
4.25% Exchangeable Senior Notes    
Carrying amount and estimated fair value of debt    
Carrying Value 0 572
Carrying Amount    
Carrying amount and estimated fair value of debt    
Variable-rate debt 556,457 639,877
Carrying Value 2,130,170 1,920,057
Carrying Amount | Unsecured senior notes    
Carrying amount and estimated fair value of debt    
Fixed-rate debt 1,187,928 890,862
Carrying Amount | Other fixed-rate debt    
Carrying amount and estimated fair value of debt    
Fixed-rate debt 385,785 389,318
Total Estimated Fair Value    
Carrying amount and estimated fair value of debt    
Variable-rate debt 557,753 642,091
Carrying Value 2,105,775 1,900,067
Total Estimated Fair Value | Unsecured senior notes    
Carrying amount and estimated fair value of debt    
Fixed-rate debt 1,202,956 901,599
Total Estimated Fair Value | Other fixed-rate debt    
Carrying amount and estimated fair value of debt    
Fixed-rate debt $ 345,066 $ 356,377