INVESTMENTS IN RESIDENTIAL MORTGAGE LOANS - Performing Loans Past Due (Details) - Residential Portfolio Segment - Performing Loans	Dec. 31, 2017
Investment [Line Items]
Delinquency Status	100.00%
Current
Investment [Line Items]
Delinquency Status	84.20%
30-59
Investment [Line Items]
Delinquency Status	6.60%
60-89
Investment [Line Items]
Delinquency Status	2.60%
90-119
Investment [Line Items]
Delinquency Status	1.50%
120
Investment [Line Items]
Delinquency Status	5.10%