REAL ESTATE AND RELATED LEASE INTANGIBLES, NET - Additional Information (Details) - USD ($)							1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 18, 2019	Dec. 16, 2019	May 01, 2019	Feb. 27, 2019	Feb. 06, 2019	Jan. 10, 2019	Dec. 31, 2019	Feb. 28, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Foreclosed properties held in real estate							$ 89,500,000			$ 89,500,000	$ 6,300,000
Proceeds from lease prepayments						$ 10,000,000.0
Mortgage loan and financing related to property sales					$ 6,600,000
Gain (loss) on extinguishment/defeasance of debt					$ (1,100,000)					(1,070,000)	(4,392,000)	$ (73,000)
Impairment of real estate									$ 1,400,000	1,350,000	0	0
Operating lease income			$ 3,900,000							106,366,000
Loss on sale of real estate			3,500,000
Depreciation and amortization			400,000							38,511,000	41,959,000	40,332,000
Loss on sale of real estate			$ 20,000
Unbilled rent receivables							900,000			900,000	800,000
Unencumbered real estates							59,200,000			59,200,000	$ 58,600,000
Real estate operating income										$ 2,600,000
Weighted average amortization period for intangible assets acquired										34 years 2 months 12 days	25 years 1 month 6 days
Revenues from acquisitions										$ 600,000	$ 5,300,000
Net earnings (loss)										(2,300,000)	2,400,000
Real estate acquired through foreclosure, fair value							84,150,000			84,150,000
Gain resulting from foreclosure of loan										2,250,000	$ 0	$ 0
Fort Worth and Arlington, TX | Real Estate Acquired in Satisfaction of Debt
Business Acquisition [Line Items]
Gain resulting from foreclosure of loan							0
Omaha, NE | Real Estate Acquired in Satisfaction of Debt
Business Acquisition [Line Items]
Gain resulting from foreclosure of loan								$ 0
Diversified | San Diego, CA
Business Acquisition [Line Items]
Real estate acquired through foreclosure, net basis							40,000,000.0			40,000,000.0
Real estate acquired through foreclosure, fair value		$ 42,300,000					42,250,000			42,250,000
Terminal capitalization rate	5.75%	8.50%
Discount rate		10.50%
Diversified | San Diego, CA | Real Estate Acquired in Satisfaction of Debt
Business Acquisition [Line Items]
Mortgage loan receivable										33,900,000
Gain resulting from foreclosure of loan							2,300,000
Diversified | San Diego, CA | First mortgage loans
Business Acquisition [Line Items]
Mortgage loan receivable										5,700,000
Diversified | Arlington, TX
Business Acquisition [Line Items]
Real estate acquired through foreclosure, fair value	$ 10,900,000
Diversified | Fort Worth and Arlington, TX
Business Acquisition [Line Items]
Real estate acquired through foreclosure, net basis							22,600,000			22,600,000
Real estate acquired through foreclosure, fair value							23,700,000			23,700,000
Assumed liabilities							$ (900,000)			$ (900,000)
Terminal capitalization rate	6.00%
Diversified | Fort Worth, TX
Business Acquisition [Line Items]
Real estate acquired through foreclosure, fair value	$ 12,800,000
Diversified | Omaha, NE
Business Acquisition [Line Items]
Real estate acquired through foreclosure, net basis								17,900,000
Real estate acquired through foreclosure, fair value				$ 18,200,000				$ 18,200,000
Terminal capitalization rate				8.75%
Discount rate				10.25%
Assets Leased to Others
Business Acquisition [Line Items]
Property book value									5,600,000
Accumulated depreciation and amortization									$ 2,700,000