Real Estate (Schedule of Transactions Related to Properties Held for Sale/Conveyance) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Real Estate Properties [Line Items]
Gain on Sale/Reversal of Impairment	$ 49,904,000	$ 4,396,000	$ 2,942,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Real Estate Properties [Line Items]
Sales Price	100,723,500	21,928,000	19,378,000
Gain on Sale/Reversal of Impairment	$ 51,753,000	$ 4,396,000	$ 2,942,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Metro Square [Member]
Real Estate Properties [Line Items]
Location		Owings Mills, MD
Date Sold		Jul. 09, 2020
Sales Price		$ 4,288,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Maxatawny Marketplace [Member]
Real Estate Properties [Line Items]
Location			Maxatawny, PA
Date Sold			Feb. 15, 2019
Sales Price			$ 10,330,000
Gain on Sale/Reversal of Impairment			$ 101,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Kempsville Crossing [Member]
Real Estate Properties [Line Items]
Location	Virginia Beach, VA
Date Sold	Feb. 24, 2021
Sales Price	$ 1,300,000
Gain on Sale/Reversal of Impairment	$ 1,047,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Oakland Mills Outparcel Building [Member]
Real Estate Properties [Line Items]
Location		Columbia, MD
Date Sold		Sep. 17, 2020
Sales Price		$ 1,050,000
Gain on Sale/Reversal of Impairment		$ 643,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Fort Washington Center [Member]
Real Estate Properties [Line Items]
Location			Fort Washington, PA
Date Sold			Jun. 26, 2019
Sales Price			$ 9,048,000
Gain on Sale/Reversal of Impairment			$ 2,841,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | The Commons [Member]
Real Estate Properties [Line Items]
Location	Dubois, PA
Date Sold	May 05, 2021
Sales Price	$ 9,761,000
Gain on Sale/Reversal of Impairment	$ 1,849,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Glen Allen Shopping Center [Member]
Real Estate Properties [Line Items]
Location		Glen Allen, VA
Date Sold		Oct. 08, 2020
Sales Price		$ 8,540,000
Gain on Sale/Reversal of Impairment		$ 1,780,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Camp Hill Shopping Center [Member]
Real Estate Properties [Line Items]
Location	Camp Hill, PA
Date Sold	Jun. 21, 2021
Sales Price	$ 89,662,500
Gain on Sale/Reversal of Impairment	$ 48,857,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Pine Grove Plaza Outparcel Building [Member]
Real Estate Properties [Line Items]
Location		Brown Mills, NJ
Date Sold		Nov. 02, 2020
Sales Price		$ 1,100,000
Gain on Sale/Reversal of Impairment		$ 565,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Suffolk Plaza [Member]
Real Estate Properties [Line Items]
Location		Suffolk, VA
Date Sold		Dec. 10, 2020
Sales Price		$ 6,950,000
Gain on Sale/Reversal of Impairment		$ 1,408,000