SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Principles of Consolidation and Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2018 variable_interest_entity Investment
Variable Interest Entity [Line Items]
Number of investments in loans accounted for as real estate joint ventures | Investment	0
Primary Beneficiary
Variable Interest Entity [Line Items]
Number of VIEs	5
Exchange Accommodation Titleholder | Primary Beneficiary
Variable Interest Entity [Line Items]
Number of VIEs	4
Skilled Nursing Transitional Care Facilities | Primary Beneficiary
Variable Interest Entity [Line Items]
Number of VIEs	1