FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value of Financial Instruments Not Recorded at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount
Liabilities:
Mortgages payable	$ 414,806	$ 414,760
Junior subordinated notes	25,153	25,133
Carrying Amount | Loans receivable subject to credit risk
Assets:
Loans receivable	48,747	58,904
Carrying Amount | SBA 7(a) loans receivable, subject to secured borrowings
Assets:
Loans receivable	21,944	21,728
Carrying Amount | Commercial mortgage loans
Assets:
Loans receivable	0	424
Fair Value, Measurements, Nonrecurring | Estimated Fair Value | Level 3
Liabilities:
Mortgages payable	407,997	413,819
Junior subordinated notes	24,308	24,162
Fair Value, Measurements, Nonrecurring | Estimated Fair Value | Level 3 | Loans receivable subject to credit risk
Assets:
Loans receivable	50,412	61,277
Fair Value, Measurements, Nonrecurring | Estimated Fair Value | Level 3 | SBA 7(a) loans receivable, subject to secured borrowings
Assets:
Loans receivable	22,366	22,157
Fair Value, Measurements, Nonrecurring | Estimated Fair Value | Level 3 | Commercial mortgage loans
Assets:
Loans receivable	$ 0	$ 424