INCOME PROPERTIES - Dispositions and Impairment Charges (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) ft² building property	Mar. 26, 2018 USD ($)
Dispositions of Income Properties
Number of properties in the disposal group | property	4
Daytona Beach, FL
Dispositions of Income Properties
Sales price | $		$ 11,400,000
Concierge Office Building
Dispositions of Income Properties
Area of real estate property	22,012
Williamson Business Park office building
Dispositions of Income Properties
Area of real estate property	15,360
Area of real estate property leased	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	30,720
Number of office building | building	2