Debt, Net (Details 2) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Carrying amount and estimated fair value of debt
Carrying Value	$ 2,094,486	$ 2,077,752
Carrying Amount
Carrying amount and estimated fair value of debt
Variable-rate debt	588,116	609,194
Carrying Value	2,094,486	2,077,752
Carrying Amount | Unsecured senior notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	1,186,672	1,185,842
Carrying Amount | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Fixed-rate debt	319,698	282,716
Total Estimated Fair Value
Carrying amount and estimated fair value of debt
Variable-rate debt	592,032	610,987
Carrying Value	2,148,333	2,114,636
Total Estimated Fair Value | Unsecured senior notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	1,227,235	1,211,658
Total Estimated Fair Value | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Fixed-rate debt	$ 329,066	$ 291,991