Fair Value Measurements and Disclosures (Details 1) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Carrying Value | Secured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	[1]	$ 378,080	$ 380,835
Carrying Value | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	[1]	1,845,313	1,844,634
Carrying Value | Line of Credit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	[1]	75,000	0
Fair Value (Level 2) [Member] | Fair Value | Secured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	[1]	388,113	391,611
Fair Value (Level 2) [Member] | Fair Value | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	[1]	1,948,299	1,898,863
Fair Value (Level 2) [Member] | Fair Value | Line of Credit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	[1]	$ 75,018	$ 0

[1] Fair value calculated using Level II inputs, which are based on model-derived valuations in which significant inputs and significant value drivers are observable in active markets.