Indebtedness - Summary of Indebtedness at Estimated Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	$ 602,927		$ 677,890
Senior Unsecured Debt, Net, Carrying Amount	364,837		445,916
Unsecured Term Loan, Carrying Amount	200,000		0
Unsecured Credit Facility, Carrying Amount	176,000		173,000
Total, Carrying Amount	1,343,764		1,296,806
Total, Fair Value	1,418,446		1,340,695
Mortgages
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	602,927		677,890
Mortgage Loans Payable, Net, Fair Value	642,936		684,914
Senior Unsecured Notes
Debt Disclosure [Line Items]
Senior Unsecured Debt, Net, Carrying Amount	364,837		445,916
Senior Unsecured Debt, Net, Fair Value	398,655		482,781
Unsecured Term Loan
Debt Disclosure [Line Items]
Unsecured Term Loan, Carrying Amount	200,000	[1]
Unsecured Term Loan, Fair Value	200,597
Unsecured Credit Facility
Debt Disclosure [Line Items]
Unsecured Credit Facility, Carrying Amount	176,000	[2]	173,000	[2]
Unsecured Credit Facility, Fair Value	$ 176,258		$ 173,000

[1] We entered into interest rate protection agreements, with an aggregate notional value of $200,000, to effectively convert the variable rate to a fixed rate. See Note 10.

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