Fair Value of Financial Instruments Schedule of the aggregate carrying value of debt and estimates of fair value (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term loan and credit facility	$ 355,600	$ 325,000
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term loan and credit facility	355,600	325,000
Mortgage notes payable | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable at Fair Value Measurement Date	1,005,569	883,112
Mortgage notes payable | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable at Fair Value Measurement Date	1,016,992	900,064
Senior unsecured notes | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable at Fair Value Measurement Date	236,999	0
Senior unsecured notes | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable at Fair Value Measurement Date	$ 253,469	$ 0