Mortgage Loans Payable and Unsecured Credit Facilities (Schedule of Mortgage Loans Payable Repaid) (Details) - Mortgage Loans Payable [Member]	12 Months Ended
	Dec. 31, 2018 USD ($)
East River Park [Member]
Debt Instrument [Line Items]
Repayment date	Aug. 10, 2018
Principal payoff amount	$ 18,772,000
Colonial Commons [Member]
Debt Instrument [Line Items]
Repayment date	Aug. 24, 2018
Principal payoff amount	$ 24,108,000
Shoppes at Arts District [Member]
Debt Instrument [Line Items]
Repayment date	Aug. 24, 2018
Principal payoff amount	$ 8,114,000
The Point [Member]
Debt Instrument [Line Items]
Repayment date	Sep. 06, 2018
Principal payoff amount	$ 27,003,000