Fair Value Measurements and Disclosures (Details 1) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Carrying value [Member] | Secured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	$ 472,772	$ 380,835
Carrying value [Member] | Unsecured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	1,847,351	1,844,634
Fair value [Member] | Secured debt [Member] | Fair value (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	469,234	391,611
Fair value [Member] | Unsecured debt [Member] | Fair value (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	$ 1,900,487	$ 1,898,863