RESIDENTIAL MORTGAGE LOAN SECURITIZATION TRUSTS - Narrative (Details) - Residential mortgage loans - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investment in Multi-Family MBS, carrying value	$ 5,413,720	$ 0
Multi-family mortgage loans held in securitization trusts, unpaid principal balance	118,884,113
Multi-Family Securitized Debt Obligations, Unpaid Principal Balance	$ 118,884,113

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