Fair Value Measurements and Disclosures (Details 1) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying value [Member] | Secured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt, net	$ 336,866	$ 340,800
Carrying value [Member] | Unsecured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt, net	2,207,049	2,006,263
Carrying value [Member] | Line of credit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt, net	330,000	0
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, net	331,313	346,858
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, net	2,173,366	2,077,199
Fair value (level 2) [Member] | Fair value [Member] | Line of credit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt, net	$ 330,221	$ 0