INCOME PROPERTIES - 2017 Acquisitions and Dispositions (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) ft² a property
2017 dispositions of income property subject to a lease | Sold
Dispositions
Number of properties in the disposal group | property	0
Commercial
Acquisitions of Income Properties
Area of real estate property | ft²	228,520
Purchase price	$ 40,040,000
2017 acquisitions of income property subject to a lease | Commercial
Acquisitions of Income Properties
Aggregate acquisition cost including capitalized acquisition costs	40,700,000
Land acquired	18,000,000
Buildings and improvements acquired	19,300,000
Intangible assets acquired	4,900,000
Intangible liabilities assumed	$ 1,500,000
Weighted average amortization period of intangible assets	9 years 9 months 18 days
Weighted average amortization period of intangible liabilities	9 years 9 months 18 days
2017 acquisitions of income property subject to a lease | Commercial | Tampa, Florida
Acquisitions of Income Properties
Acres | a	5.3
Purchase price	$ 14,650,000
Percentage Leased	100.00%
Remaining Lease Term	13 years 10 months 24 days
2017 acquisitions of income property subject to a lease | Single-tenant
Acquisitions of Income Properties
Number of real estate properties | property	3
2017 acquisitions of income property subject to a lease | Single-tenant | Sarasota, Florida
Acquisitions of Income Properties
Area of real estate property | ft²	18,120
Acres | a	1.2
Purchase price	$ 4,075,000
Percentage Leased	100.00%
Remaining Lease Term	5 years
2017 acquisitions of income property subject to a lease | Single-tenant | Boston, Massachusetts
Acquisitions of Income Properties
Area of real estate property | ft²	22,500
Acres | a	2.6
Purchase price	$ 6,315,000
Percentage Leased	100.00%
Remaining Lease Term	11 years 9 months 18 days
2017 acquisitions of income property subject to a lease | Single-tenant | Tampa, Florida
Acquisitions of Income Properties
Area of real estate property | ft²	45,000
2017 acquisitions of income property subject to a lease | Multi-tenant
Acquisitions of Income Properties
Number of real estate properties | property	2
2017 acquisitions of income property subject to a lease | Multi-tenant | Fort Worth, Texas
Acquisitions of Income Properties
Area of real estate property | ft²	136,185
Acres | a	10.3
Purchase price	$ 15,000,000
Percentage Leased	96.00%
Remaining Lease Term	4 years 1 month 6 days
2017 acquisitions of income property subject to a lease | Multi-tenant | Tampa, Florida
Acquisitions of Income Properties
Area of real estate property | ft²	6,715