Debt and Derivative Instruments (Schedule of Mortgages and Credit Facility Payable) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Mortgage Loans On Real Estate [Line Items]
Mortgages payable	$ 576,792	$ 576,836
Credit facility payable	74,500	31,000
Total debt before unamortized mortgage premiums and debt issuance costs including impact of interest rate swaps	651,292	607,836
Add: Unamortized mortgage premiums	2,857	3,080
Less: Unamortized debt issuance costs	(4,615)	(4,891)
Total debt	$ 649,534	$ 606,025
Mortgages Payable, Weighted Average Interest Rate	3.65%	3.62%
Credit Facilities Payable, Weighted Average Interest Rate	2.34%	2.26%
Total debt before unamortized mortgage premiums and debt issuance costs including impact of interest rate swaps, Weighted Average Interest Rate	3.50%	3.55%
Fixed rate mortgages payable [Member]
Mortgage Loans On Real Estate [Line Items]
Mortgages payable	$ 178,301	$ 178,345
Mortgages Payable, Weighted Average Interest Rate	4.31%	4.31%
Variable rate mortgages payable with swap agreements [Member]
Mortgage Loans On Real Estate [Line Items]
Mortgages payable	$ 354,488	$ 354,488
Mortgages Payable, Weighted Average Interest Rate	3.43%	3.42%
Variable rate mortgages payable [Member]
Mortgage Loans On Real Estate [Line Items]
Mortgages payable	$ 44,003	$ 44,003
Mortgages Payable, Weighted Average Interest Rate	2.71%	2.50%