INCOME PROPERTIES - Dispositions and Impairment Charges (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) ft² property	Dec. 31, 2018 USD ($) ft² building property	Dec. 31, 2017 USD ($) property	Feb. 21, 2019 USD ($) ft²	Mar. 26, 2018 USD ($)
Dispositions of Income Properties
Number of properties in the disposal group | property		4
Area of real estate property | ft²	502,626
Gain on sale of properties (in dollars per share)	$ 20.60		$ 3.51
Number of real estate properties | property	34
Daytona Beach, FL
Dispositions of Income Properties
Sales price					$ 11,400,000
Concierge Office Building
Dispositions of Income Properties
Area of real estate property | ft²		22,012
Williamson Business Park office building
Dispositions of Income Properties
Area of real estate property | ft²		15,360
Area of real estate property leased | ft²		7,600
Gain on Sale		$ 3,700,000
Gain on sale of properties (in dollars per share)		$ 0.49
Lease term		5 years
Mason Commerce Center
Dispositions of Income Properties
Area of real estate property | ft²		30,720
Number of office building | building		2
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Whole Foods | Sarasota, FL
Dispositions of Income Properties
Sales price				$ 24,600,000
Area of real estate property | ft²				59,000
Gain on Sale	$ 6,900,000
Gain on sale of properties (in dollars per share)	$ 0.96
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 2017 dispositions of income property subject to a lease
Dispositions of Income Properties
Number of properties in the disposal group | property			0