REAL ESTATE AND RELATED LEASE INTANGIBLES, NET - Additional Information (Details) - USD ($) $ in Thousands					3 Months Ended			6 Months Ended
		May 01, 2019	Feb. 06, 2019	Jan. 10, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Feb. 28, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Impairment of real estate					$ 0	$ 1,400	$ 0	$ 1,350	$ 0
Foreclosed properties held in real estate					24,100			24,100			$ 6,300
Gross intangible assets					158,900			158,900			162,000
Accumulated amortization					59,800			59,800			57,700
Net intangible assets					99,000			99,000			104,300
Unamortized favorable/unfavorable lease intangibles					4,700			4,700			5,500
Increase in operating lease income, amortization of below market lease intangibles acquired					500		700	1,000	1,300
Proceeds from lease prepayments				$ 10,000
Real estate and related lease intangibles, net	[1]				984,377			984,377			998,022
Accumulated depreciation and amortization					189,172			189,172			173,938
Mortgage loan and financing related to property sales			$ 6,600
Gain (loss) on extinguishment/defeasance of debt			$ (1,100)		0		0	(1,070)	(69)
Operating lease income		$ 3,900			27,780			56,701
Loss on sale of real estate		3,500
Depreciation and amortization		400			9,935		10,656	20,162	$ 21,479
Loss on sale of real estate		$ 20
Unbilled rent receivables					1,400			1,400			800
Unencumbered real estates					71,500			71,500			58,600
Real estate operating income					800			1,000
Real estate acquired through foreclosure					18,200			18,200
Unamortized discounts included in mortgage loan receivables held for investment, at amortized cost					300			$ 300			$ 500
Weighted average amortization period for intangible assets acquired								37 months	18 years 4 months 24 days
Revenues from acquisitions					62		1,400	$ 79	$ 1,400
Net earnings (loss)					(1,200)		800	(1,500)	800
Above Market Leases
Business Acquisition [Line Items]
Decrease in operating lease income, amortization of above market lease intangibles acquired					200		$ 200	600	$ 400
Real Estate Acquired in Satisfaction of Debt
Business Acquisition [Line Items]
Accrued interest								200
Loans in default, no losses expected					17,800			17,800
Unamortized discounts included in mortgage loan receivables held for investment, at amortized cost					100			100
Real Estate Acquired in Satisfaction of Debt | Omaha, Nebraska
Business Acquisition [Line Items]
Real estate acquired through foreclosure					$ 18,200			$ 18,200		$ 18,200
Assets Leased to Others
Business Acquisition [Line Items]
Property book value						5,600
Other Depreciation and Amortization						$ 2,700

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.