Fair Value Measurements and Disclosures (Details 1) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Carrying Value [Member] | Secured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	$ 467,758	$ 472,772
Carrying Value [Member] | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	2,097,083	1,847,351
Fair Value (Level 2) [Member] | Fair Value [Member] | Secured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	467,782	469,234
Fair Value (Level 2) [Member] | Fair Value [Member] | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	$ 2,172,095	$ 1,900,487