Quarterly report pursuant to Section 13 or 15(d)

Debt, Net (Details 2)

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Debt, Net (Details 2) - USD ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Carrying amount and estimated fair value of debt    
Carrying Value $ 2,140,212 $ 2,077,752
Carrying Amount    
Carrying amount and estimated fair value of debt    
Variable-rate debt 672,693 609,194
Carrying Value 2,140,212 2,077,752
Carrying Amount | Unsecured senior notes    
Carrying amount and estimated fair value of debt    
Fixed-rate debt 1,186,255 1,185,842
Carrying Amount | Other fixed-rate debt    
Carrying amount and estimated fair value of debt    
Fixed-rate debt 281,264 282,716
Total Estimated Fair Value    
Carrying amount and estimated fair value of debt    
Variable-rate debt 677,203 610,987
Carrying Value 2,182,752 2,114,636
Total Estimated Fair Value | Unsecured senior notes    
Carrying amount and estimated fair value of debt    
Fixed-rate debt 1,216,295 1,211,658
Total Estimated Fair Value | Other fixed-rate debt    
Carrying amount and estimated fair value of debt    
Fixed-rate debt $ 289,254 $ 291,991