BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)			1 Months Ended	2 Months Ended	3 Months Ended										8 Months Ended		12 Months Ended						20 Months Ended
	Dec. 14, 2018	Apr. 30, 2017 USD ($) shares	Aug. 31, 2017 property	Dec. 31, 2018 USD ($) $ / shares shares	Oct. 31, 2018 USD ($) $ / shares	Jul. 31, 2018 USD ($) $ / shares	Apr. 30, 2018 USD ($) $ / shares shares	Jan. 31, 2018 USD ($) $ / shares	Oct. 31, 2017 USD ($) $ / shares	Jul. 31, 2017 USD ($) $ / shares	Apr. 30, 2017 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares	Oct. 31, 2016 USD ($) $ / shares	Jul. 31, 2016 USD ($) $ / shares	Dec. 31, 2018 USD ($) property $ / shares shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2018 USD ($) shares	Apr. 30, 2018 USD ($) property $ / shares shares	Dec. 31, 2017	Apr. 30, 2017 USD ($) property $ / shares shares	Dec. 31, 2016	Apr. 30, 2016 USD ($) property $ / shares shares	Dec. 31, 2018 USD ($) shares	Dec. 27, 2018 shares	Dec. 26, 2018 shares
BASIS OF PRESENTATION [Abstract]
Interest in operating partnership (in hundredths)		88.60%		89.70%			89.40%				88.60%				89.70%		89.70%	89.40%		88.60%			89.70%
Percentage of general interest partnership (in hundredths)		100.00%		100.00%			100.00%				100.00%				100.00%		100.00%	100.00%		100.00%			100.00%
Reverse stock split, conversion ratio	0.10
Common Shares of Beneficial Interest, shares issued (in shares) | shares		12,119,930		11,942,372			11,952,598				12,119,930				11,942,372		11,942,372	11,952,598		12,119,930			11,942,372	11,900,000	119,400,000
Reverse stock split, units (in shares) | shares																								1,400,000	13,700,000
REAL ESTATE INVESTMENTS [Abstract]
Real estate investments		$ 1,121,385,000		$ 1,289,476,000			$ 1,380,245,000				$ 1,121,385,000				$ 1,289,476,000		$ 1,289,476,000	$ 1,380,245,000		$ 1,121,385,000			$ 1,289,476,000
Construction period interest capitalized															0			4,000		431,000		$ 4,900,000
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments															1,221,000			18,065,000		57,028,000		5,983,000
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
Net income				$ (3,892,000)	$ (6,264,000)	$ 1,211,000	$ (22,579,000)	$ 134,331,000	$ 6,360,000	$ (13,550,000)	$ 27,994,000	$ 19,172,000	$ 8,722,000	$ (24,522,000)	$ (8,945,000)	$ 117,461,000		$ 104,562,000		$ 31,366,000		$ 60,492,000
Net income (loss) per common share - basic & diluted (in dollars per share) | $ / shares				$ (0.33)	$ (0.52)	$ 0.10	$ (1.89)	$ 11.22	$ 0.53	$ (1.12)	$ 2.33	$ 1.58	$ 0.72	$ (2.02)	$ (0.75)	$ 9.78		$ 8.71		$ 2.58		$ 4.91
HELD FOR SALE [Abstract]
Number of year after date of acquisition related to adjustment of real estate preliminary allocations of purchase price															1 year
RESTRICTED CASH [Abstract]
Restricted cash		27,981,000		$ 5,464,000			$ 4,225,000				$ 27,981,000				$ 5,464,000		5,464,000	$ 4,225,000		$ 27,981,000			5,464,000
PROPERTY AND EQUIPMENT [Abstract]
Property and equipment cost		2,100,000		2,200,000			2,100,000				2,100,000				2,200,000		2,200,000	2,100,000		2,100,000			2,200,000
Accumulated depreciation		$ 1,200,000		1,400,000			1,300,000				$ 1,200,000				$ 1,400,000		$ 1,400,000	$ 1,300,000		$ 1,200,000			1,400,000
INCOME TAXES [Abstract]
Minimum dividend distribution percentage															90.00%
Dividend distribution percentage (in hundredths)															90.00%			90.00%		90.00%		90.00%
Distribution of federal income tax (in hundredths)																	100.00%		14.59%		12.43%
Distribution of capital gain (in hundredths)																			48.87%		87.57%
Distribution made as return of capital (in hundredths)																			36.54%
MORTGAGE LOANS RECEIVABLE AND NOTES RECEIVABLE [Abstract]
Number of real estate properties sold | property																		28
Mortgage loans receivable				10,400,000			11,000,000								$ 10,400,000		$ 10,400,000	$ 11,000,000					$ 10,400,000
Interest income															1,168,000	$ 432,000		1,197,000		$ 366,000		$ 78,000
Proceeds from collection of loans receivable															545,000			0		0		0
GAIN ON BARGAIN PURCHASE [Abstract]
Gain on bargain purchase															$ 0	$ 0		$ 0		0		$ 3,424,000
Buildings and Improvements | Minimum
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)															10 years
Buildings and Improvements | Maximum
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)															37 years
Furniture, Fixtures and Equipment | Minimum
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)															5 years
Furniture, Fixtures and Equipment | Maximum
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)															10 years
Renovations and Improvements | Minimum
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)															5 years
Renovations and Improvements | Maximum
REAL ESTATE INVESTMENTS [Abstract]
Estimated useful life of assets (in years)															10 years
Minot, ND - property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																				$ 2,900,000
Multi-family Residential Properties
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																		1		16
Multi-family Residential Properties | Grand Forks, North Dakota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		$ 12,200,000
Multi-family Residential Properties | Williston, ND - property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																				3
Multi-family Residential Properties | Williston, ND - property 1
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 | Williston, ND - property 2
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																				$ 5,800,000
Multi-family Residential Properties | Williston, ND - property 3
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
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																		3
Land
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																		4		2		2
Land | Grand Forks, North Dakota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		$ 1,500,000
Land | Minot, ND - property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																				1
Land | Bismark, North Dakota - First Property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		$ 256,000
Land | Bismark, North Dakota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																		2
Land | Bismark, North Dakota - Second Property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		$ 709,000
Land | Williston, ND - property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		428,000		$ 2,800,000
Number of impaired properties | property																				1
Interest in joint venture		70.00%									70.00%									70.00%
Land | River Falls Wisconsin
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																						$ 162,000
Industrial | Bloomington, Minnesota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		1,400,000
Industrial | Woodbury, Minnesota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		922,000
Retail Site | Minot, ND - property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																		$ 630,000
Office
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																						1
Commercial Healthcare
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																						1
Multi-Family Residential
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																						8
MORTGAGE LOANS RECEIVABLE AND NOTES RECEIVABLE [Abstract]
Interest rate on mortgages payable						6.00%
Loan commitment										$ 16,200,000
Multi-Family Residential | St Cloud Minnesota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																						$ 1,900,000
Number of impaired properties | property																						8
Office Property | Eden Prairie Minnesota
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																						$ 440,000
Assets Held for Sale
HELD FOR SALE [Abstract]
Number of real estate properties classified as held for sale | property															0			0
Assets Held for Sale | Multi-family Residential Properties
HELD FOR SALE [Abstract]
Number of real estate properties classified as held for sale | property																				13
Assets Held for Sale | Multi-family Residential Properties | Minot, ND - property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Number of impaired properties | property																				13
Assets Held for Sale | Retail Site
HELD FOR SALE [Abstract]
Number of real estate properties classified as held for sale | property																				2
Assets Held for Sale | Commercial Healthcare
HELD FOR SALE [Abstract]
Number of real estate properties classified as held for sale | property																				2
Assets Held for Sale | Medical Property | Sartell, Minnesota, Healthcare Property
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																						1,900,000
Discontinued Operations
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																						440,000
Discontinued Operations | Land | Grand Chute, Wisconsin, Unimproved Land
IMPAIRMENT OF LONG-LIVED ASSETS [Abstract]
Impairment of real estate investments																						1,600,000
Discontinued Operations, Disposed of by Sale
MORTGAGE LOANS RECEIVABLE AND NOTES RECEIVABLE [Abstract]
Interest income															$ 0			$ 661,000		$ 2,179,000		2,179,000
Discontinued Operations, Disposed of by Sale | Multi-Family Residential
MORTGAGE LOANS RECEIVABLE AND NOTES RECEIVABLE [Abstract]
Number of real estate properties sold | property			13												13
Interest rate on mortgages payable			5.50%
Interest income															$ 448,000			372,000
Number of real estate properties released | property															1
Service Life
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
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 | Minimum
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
Useful life		20 years																					10 years
Service Life | Maximum
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
Useful life		40 years																					37 years
Service Life | Property With Previous Nine Year Life
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
Useful life		9 years
Service Life | Property With Previous Nine Year Life | Minimum
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
Useful life																							5 years
Service Life | Property With Previous Nine Year Life | Maximum
CHANGE IN DEPRECIABLE LIVES OF REAL ESTATE ASSETS [Abstract]
Useful life																							10 years
Escrow Deposits
RESTRICTED CASH [Abstract]
Restricted cash		$ 4,300,000		$ 5,500,000			$ 4,200,000				$ 4,300,000				$ 5,500,000		$ 5,500,000	$ 4,200,000		4,300,000			$ 5,500,000
Tax-Deferred Exchange Proceeds
RESTRICTED CASH [Abstract]
Restricted cash		$ 23,700,000									$ 23,700,000									$ 23,700,000
187 unit - Avalon Cove - Rochester, MN
GAIN ON BARGAIN PURCHASE [Abstract]
Total acquisition costs																						36,300,000
Form of consideration, cash																						$ 15,000,000
Shares exchanged (in shares) | shares																						250,000
Shares exchanged																						$ 17,800,000
Share price (in dollars per share) | $ / shares																						$ 70.90
Gain on bargain purchase																						$ 3,400,000