FAIR VALUE OF FINANCIAL INSTRUMENTS - Unobservable Inputs (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Mortgages Payable | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	4.18%	4.60%
Mortgages Payable | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	4.38%	4.72%
Junior Subordinated Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, discount rate	5.08%	4.83%
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	8.75%	8.25%
Fair value inputs, prepayment rates	5.80%	5.80%
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	13.75%	13.25%
Fair value inputs, prepayment rates	20.00%	20.00%
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%	6.70%
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	20.00%	20.00%