BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Impairment of Long-Lived Assets (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments	$ 0	$ 0	$ 0	$ 17,809,000
Grand Forks, North Dakota | Apartment Building
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				12,200,000
Grand Forks, North Dakota | Land
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				1,500,000
Bloomington, Minnesota | Industrial Property
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				1,400,000
Woodbury, Minnesota | Industrial Property
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				922,000,000
Property In Minot ND | Retail Property
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				630,000,000
Williston, North Dakota | Land
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				428,000
Bismarck, North Dakota | Land
Long Lived Assets Held-for-sale [Line Items]
Impairment of real estate investments				$ 709,000