Real Estate (Schedule of Transactions Related to Properties Held for Sale/Conveyance) (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations [Member] - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Real Estate Properties [Line Items]
Sales Price	$ 19,378,000	$ 19,600,000	$ 12,850,000
Gain on Sale	$ 2,942,000	$ 4,864,000	$ 7,099,000
Maxatawny Marketplace [Member]
Real Estate Properties [Line Items]
Location	Maxatawny, PA
Date Sold	Feb. 15, 2019
Sales Price	$ 10,330,000
Gain on Sale	$ 101,000
Mechanicsburg Center [Member]
Real Estate Properties [Line Items]
Location		Mechanicsburg, PA
Date Sold		Aug. 28, 2018
Sales Price		$ 16,100,000
Gain on Sale		$ 4,864,000
West Bridgewater Plaza [Member]
Real Estate Properties [Line Items]
Location		West Bridgewater, MA
Date Sold		Sep. 28, 2018
Sales Price		$ 3,500,000
Outparcel Building Adjacent to Camp Hill [Member]
Real Estate Properties [Line Items]
Location			Camp Hill, PA
Date Sold			Feb. 01, 2017
Sales Price			$ 10,650,000
Gain on Sale			$ 7,099,000
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	$ 2,841,000
Fredericksburg Way [Member]
Real Estate Properties [Line Items]
Location			Fredericksburg, VA
Date Sold			Dec. 29, 2017
Sales Price			$ 2,200,000