Real Estate (Narrative) (Details) - USD ($)			12 Months Ended
	Aug. 21, 2018	Aug. 08, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate Properties [Line Items]
Capital lease obligation			$ 5,387,000
Interest only mortgage note receivable issued			3,500,000
Impairment charges			20,689,000	$ 9,538,000	$ 6,347,000
Land Parcel Adjacent To Riverview Plaza
Real Estate Properties [Line Items]
Purchase price		$ 1,000,000
Cash payments		$ 25,000
Number of OP Units issued		208,000
Senator Square [Member]
Real Estate Properties [Line Items]
Capital lease obligation	$ 5,700,000
Capital Leases obligation interest rate	5.30%
Lease monthly payment	$ 75,000
Lease expiration date	Aug. 31, 2117
Duration required to earn fair value purchase option minimum	25 years
Duration required to earn fair value purchase option maximum	33 years
Duration interval between subsequent fair value purchase option	10 years
Lease terms	The lease initially requires monthly payments of $75,000 through maturity in August 2117 unless the Company exercises one of its options to acquire the land. The first such option will be available between the 25th and 33rd anniversaries of the lease, depending on certain property benchmarks, with additional purchase options every 10 years thereafter during the lease term. The lease also provides for 1.5% annual increases which begin on approximately the 8th anniversary of the lease, depending on the aforementioned property benchmarks.
Lease annual increase percentage	1.50%
Lease period of aforementioned property benchmarks	8 years
Lease payment mnimum duration period required to adjustment purchase options	25 years
Lease payment maximum duration period required to adjustment purchase options	50 years
Interest only mortgage note receivable issued	$ 3,500,000
Interest only mortgage note receivable, interest rate	4.50%
Senator Square [Member] | Minimum [Member]
Real Estate Properties [Line Items]
Mortgage note receivable maturity date	26 years 6 months
Senator Square [Member] | Maximum [Member]
Real Estate Properties [Line Items]
Mortgage note receivable maturity date	34 years 6 months
West Bridgewater Plaza [Member]
Real Estate Properties [Line Items]
Impairment charges			9,400,000
Fredericksburg Way [Member]
Real Estate Properties [Line Items]
Impairment charges				$ 9,500,000
Upland Square [Member]
Real Estate Properties [Line Items]
Impairment charges					$ (6,300,000)
Real Estate Held for Sale [Member]
Real Estate Properties [Line Items]
Impairment charges			$ 11,300,000