SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) Property variable_interest_entity Segment Investment	Dec. 31, 2015 USD ($) Property Investment	Dec. 31, 2014 USD ($) Property	Oct. 01, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Acquisition costs	$ 1,100,000
Number of variable interest entities | variable_interest_entity	2
Number of investments in loans accounted for as real estate joint ventures | Investment	0	0
Number of real estate properties acquired | Property	7	24	42
Acquisition pursuit costs	$ 1,200,000	$ 7,000,000	$ 3,100,000
Impairment losses on real estate investments	29,811,000	0	$ 0
Assets held for sale	0	0
Restricted cash	9,002,000	9,813,000
Deferred financing costs, net of amortization	$ 16,452,000
Number of reportable segments | Segment	1
Cash Obligations [Member]
Property, Plant and Equipment [Line Items]
Restricted cash	$ 6,800,000	5,000,000
Land Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Land Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	40 years
Buildings and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Buildings and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	40 years
Furniture and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	1 year
Furniture and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	20 years
Forest Park - Frisco [Member]
Property, Plant and Equipment [Line Items]
Impairment losses on real estate investments	$ 29,800,000
Accounting Standards Update 2015-03 [Member] | Prepaid Expenses, Deferred Financing Costs and Other Assets, Net [Member]
Property, Plant and Equipment [Line Items]
Deferred financing costs, net of amortization		(17,300,000)
Accounting Standards Update 2015-03 [Member] | Long-term Debt [Member]
Property, Plant and Equipment [Line Items]
Deferred financing costs, net of amortization		$ 17,300,000
New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2017-01 [Member]
Property, Plant and Equipment [Line Items]
Acquisition costs				$ 300,000