FAIR VALUE OF FINANCIAL INSTRUMENTS - Unobservable Inputs (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 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	4.46%	4.15%
Mortgages Payable | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	4.49%	4.28%
Junior Subordinated Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	6.56%	5.94%
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	6.75%	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	9.25%	9.00%
Fair value inputs, prepayment rates	17.50%	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%