FAIR VALUE OF FINANCIAL INSTRUMENTS - Unobservable Inputs (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Mortgages Payable | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	4.65%	4.15%
Mortgages Payable | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	4.67%	4.28%
Junior Subordinated Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	6.59%	5.94%
SBA 7(a) loans receivable, subject to loan-backed notes | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	8.00%
Fair value inputs, prepayment rates	7.30%
SBA 7(a) loans receivable, subject to loan-backed notes | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	9.50%
Fair value inputs, prepayment rates	17.50%
SBA 7(a) loans receivable, subject to secured borrowings | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, prepayment rates	15.50%	15.50%
SBA 7(a) loans receivable, subject to secured borrowings | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, prepayment rates	17.50%	17.50%
Loans Receivable Subject to Credit Risk | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	7.25%	6.25%
Fair value inputs, prepayment rates	7.30%	7.30%
Loans Receivable Subject to Credit Risk | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	9.50%	9.00%
Fair value inputs, prepayment rates	17.50%	17.50%