BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Real Estate Properties (Details) $ / shares in Units, shares in Millions		1 Months Ended	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2017 USD ($)	Aug. 31, 2017 USD ($) property	Apr. 30, 2018 USD ($) $ / shares	Jan. 31, 2018 USD ($) $ / shares	Oct. 31, 2017 USD ($) $ / shares	Jul. 31, 2017 USD ($) $ / shares	Apr. 30, 2017 USD ($) $ / shares	Jan. 31, 2017 USD ($) $ / shares	Oct. 31, 2016 USD ($) $ / shares	Jul. 31, 2016 USD ($) $ / shares	Oct. 31, 2017 segment	Jan. 31, 2018	Apr. 30, 2018 USD ($) property $ / shares	Dec. 31, 2017	Apr. 30, 2017 USD ($) property $ / shares	Dec. 31, 2016	Apr. 30, 2016 USD ($) property segment $ / shares shares
BASIS OF PRESENTATION [Abstract]
Interest in operating partnership (in hundredths)	88.60%		89.40%				88.60%						89.40%		88.60%
Percentage of general interest partnership (in hundredths)	100.00%		100.00%				100.00%						100.00%		100.00%
Redemption basis													1
RECENT ACCOUNTING PRONOUNCEMENTS [Abstract]
Acquisition costs capitalized			$ 411,536										$ 411,536
REAL ESTATE INVESTMENTS [Abstract]
Real estate investments	$ 1,121,385,000		1,380,245,000				$ 1,121,385,000						1,380,245,000		$ 1,121,385,000
Construction period interest capitalized													4,000		431,000		$ 4,900,000
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													18,065,000		57,028,000		$ 5,983,000
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Number of reportable segments | segment											2						5
Net income			$ (22,579,000)	$ 134,331,000	$ 6,360,000	$ (13,550,000)	$ 27,994,000	$ 19,172,000	$ 8,722,000	$ (24,522,000)			$ 104,562,000		$ 31,366,000		$ 60,492,000
Net income (loss) per common share - basic & diluted (in dollars per share) | $ / shares			$ (0.19)	$ 1.12	$ 0.05	$ (0.11)	$ 0.23	$ 0.16	$ 0.07	$ (0.20)			$ 0.87		$ 0.26		$ 0.49
Held for Sale [Abstract]
Number of year after date of acquisition related to adjustment of real estate preliminary allocations of purchase price													1 year
PROPERTY AND EQUIPMENT [Abstract]
Property and equipment cost	2,100,000		$ 2,100,000				$ 2,100,000						$ 2,100,000		$ 2,100,000
Accumulated depreciation	1,200,000		1,300,000				1,200,000						1,300,000		1,200,000
RESTRICTED CASH
Restricted cash	27,981,000		4,225,000				27,981,000						$ 4,225,000		$ 27,981,000
INCOME TAXES [Abstract]
Minimum dividend distribution percentage													90.00%
Dividend distribution percentage (in hundredths)													90.00%		90.00%		90.00%
Distribution of federal income tax (in hundredths)														14.59%		12.43%
Distribution of capital gain (in hundredths)														48.87%		87.57%
Distribution made as return of capital (in hundredths)														36.54%
Financing Receivable, Net [Abstract]
Number of real estate properties sold | property													28
Mortgage loans receivable	$ 0		10,329,000				$ 0						$ 10,329,000		$ 0
Interest income													1,197,000		366,000		$ 78,000
Business Combination, Bargain Purchase [Abstract]
Gain on bargain purchase													$ 0		0		$ 3,424,000
Buildings and Improvements [Member] | Minimum [Member]
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)													10 years
Buildings and Improvements [Member] | Maximum [Member]
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)													37 years
Furniture, Fixtures and Equipment [Member] | Minimum [Member]
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)													5 years
Furniture, Fixtures and Equipment [Member] | Maximum [Member]
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)													10 years
Renovations and Improvements [Member] | Minimum [Member]
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)													5 years
Renovations and Improvements [Member] | Maximum [Member]
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)													10 years
Minot, ND - property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments															$ 2,900,000
Multi-family Residential Properties [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property													1		16
Multi-family Residential Properties [Member] | Grand Forks, North Dakota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													$ 12,200,000
Multi-family Residential Properties [Member] | Williston, ND - property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property															3
Multi-family Residential Properties [Member] | Williston, ND - property 1 [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments															$ 40,900,000
Interest in joint venture	70.00%						70.00%								70.00%
Multi-family Residential Properties [Member] | Williston, ND - property 2 [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments															$ 5,800,000
Multi-family Residential Properties [Member] | Williston, ND - property 3 [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments															$ 4,700,000
Interest in joint venture	60.00%						60.00%								60.00%
Commercial Properties [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property													3
Land [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property													4		2		2
Land [Member] | Grand Forks, North Dakota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													$ 1,500,000
Land [Member] | Minot, ND - property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property															1
Land [Member] | Bismark, North Dakota - First Property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													$ 256,000
Land [Member] | Bismark, North Dakota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property													2
Land [Member] | Bismark, North Dakota - Second Property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													$ 709,000
Land [Member] | Williston, ND - property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													428,000		$ 2,800,000
Interest in joint venture	70.00%						70.00%								70.00%
Number of impaired properties | property															1
Land [Member] | River Falls Wisconsin [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																	$ 162,000
Industrial [Member] | Bloomington, Minnesota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													1,400,000
Industrial [Member] | Woodbury, Minnesota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													922,000
Retail Site [Member] | Minot, ND - property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments													630,000
Office [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																	1
Commercial Healthcare [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																	1
Multi-Family Residential [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																	8
Financing Receivable, Net [Abstract]
Interest rate on mortgages payable												6.00%
Loan commitment						$ 16,200,000
Notes receivable			15,500,000										$ 15,500,000
Multi-Family Residential [Member] | St Cloud Minnesota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																	$ 1,900,000
Number of impaired properties | property																	8
Office Property [Member] | Eden Prairie Minnesota [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																	$ 440,000
Assets Held for Sale [Member]
Held for Sale [Abstract]
Number of real estate properties classified as held for sale | property													0
Assets Held for Sale [Member] | Multi-family Residential Properties [Member]
Held for Sale [Abstract]
Number of real estate properties classified as held for sale | property															13
Assets Held for Sale [Member] | Multi-family Residential Properties [Member] | Minot, ND - property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property															13
Assets Held for Sale [Member] | Retail Site [Member]
Held for Sale [Abstract]
Number of real estate properties classified as held for sale | property															2
Assets Held for Sale [Member] | Commercial Healthcare [Member]
Held for Sale [Abstract]
Number of real estate properties classified as held for sale | property															2
Assets Held for Sale [Member] | Medical Property [Member] | Sartell, Minnesota, Healthcare Property [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																	1,900,000
Discontinued Operations [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																	440,000
Financing Receivable, Net [Abstract]
Interest income													$ 661,000		$ 2,179,000		2,179,000
Discontinued Operations [Member] | Land [Member] | Grand Chute, Wisconsin, Unimproved Land [Member]
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																	1,600,000
Discontinued Operations [Member] | Commercial Healthcare [Member]
REAL ESTATE INVESTMENTS [Abstract]
Number of real estate properties classified as discontinued operations | property													27
Discontinued Operations, Disposed of by Sale [Member] | Multi-Family Residential [Member]
Financing Receivable, Net [Abstract]
Number of real estate properties sold | property		13
Mortgage loans receivable		$ 11,000,000
Deferred gain on sale of properties		$ 626,000
Interest rate on mortgages payable		5.50%
Interest income													$ 372,000
Service Life [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Depreciation													29,300,000
Net income													$ (29,300,000)
Net income (loss) per common share - basic & diluted (in dollars per share) | $ / shares													$ (0.22)
Service Life [Member] | Minimum [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Useful life	20 years											10 years
Service Life [Member] | Maximum [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Useful life	40 years											37 years
Service Life [Member] | Property With Previous Nine Year Life [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Useful life	9 years
Service Life [Member] | Property With Previous Nine Year Life [Member] | Minimum [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Useful life												5 years
Service Life [Member] | Property With Previous Nine Year Life [Member] | Maximum [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Useful life												10 years
Service Life [Member] | Fully Depreciated Property [Member]
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS
Depreciation						$ 9,000,000
Net income (loss) per common share - basic & diluted (in dollars per share) | $ / shares						$ (0.07)
Escrow Deposits [Member]
RESTRICTED CASH
Restricted cash	$ 4,300,000		$ 4,200,000				$ 4,300,000						$ 4,200,000		4,300,000
Tax-Deferred Exchange Proceeds [Member]
RESTRICTED CASH
Restricted cash	$ 23,700,000						$ 23,700,000								$ 23,700,000
187 unit - Avalon Cove - Rochester, MN [Member]
Business Combination, Bargain Purchase [Abstract]
Total acquisition costs																	36,300,000
Form of consideration, cash																	$ 15,000,000
Shares exchanged (in shares) | shares																	2.5
Shares exchanged																	$ 17,800,000
Share price (in dollars per share) | $ / shares																	$ 7.09
Gain on bargain purchase																	$ 3,400,000