Quarterly report pursuant to Section 13 or 15(d)

Debt, Net (Details 2)

v3.7.0.1
Debt, Net (Details 2) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Carrying Amount    
Carrying amount and estimated fair value of debt    
Long-term debt $ 1,903,657 $ 1,904,001
Carrying Amount | Unsecured senior notes    
Carrying amount and estimated fair value of debt    
Long-term debt 1,187,942 1,187,515
Carrying Amount | Other fixed-rate debt    
Carrying amount and estimated fair value of debt    
Long-term debt 154,668 155,544
Carrying Amount | Variable-rate debt    
Carrying amount and estimated fair value of debt    
Long-term debt 561,047 560,942
Estimated Fair Value    
Carrying amount and estimated fair value of debt    
Long-term debt 1,936,695 1,935,606
Estimated Fair Value | Unsecured senior notes    
Carrying amount and estimated fair value of debt    
Long-term debt 1,223,753 1,220,282
Estimated Fair Value | Other fixed-rate debt    
Carrying amount and estimated fair value of debt    
Long-term debt 156,098 156,887
Estimated Fair Value | Variable-rate debt    
Carrying amount and estimated fair value of debt    
Long-term debt $ 556,844 $ 558,437