Indebtedness - Summary of Indebtedness at Estimated Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	$ 631,137		$ 677,890
Senior Unsecured Debt, Net, Carrying Amount	364,814		445,916
Unsecured Term Loan, Carrying Amount	200,000		0
Unsecured Credit Facility, Carrying Amount	187,000		173,000
Total, Carrying Amount	1,382,951		1,296,806
Total, Fair Value	1,457,849		1,340,695
Mortgages
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	631,137		677,890
Mortgage Loans Payable, Net, Fair Value	667,095		684,914
Senior Unsecured Notes
Debt Disclosure [Line Items]
Senior Unsecured Debt, Net, Carrying Amount	364,814		445,916
Senior Unsecured Debt, Net, Fair Value	403,458		482,781
Unsecured Term Loan
Debt Disclosure [Line Items]
Unsecured Term Loan, Carrying Amount	200,000
Unsecured Term Loan, Fair Value	200,000
Unsecured Credit Facility
Debt Disclosure [Line Items]
Unsecured Credit Facility, Carrying Amount	187,000	[1]	173,000	[1]
Unsecured Credit Facility, Fair Value	$ 187,296		$ 173,000

[1] * The maturity date may be extended an additional year at our election, subject to certain restrictions.