COMMERCIAL MORTGAGE LOANS - Impaired Loans (Details) - Commercial Mortgage Loans - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Recorded Investment
With no related allowance recorded	$ 0	$ 710
With an allowance recorded	0	16,209
Unpaid Principal Balance
With no related allowance recorded	0	702
With an allowance recorded	0	16,102
Related Allowance
With an allowance recorded	0	4,884
Average Recorded Investment
With no related allowance recorded	0	237
With an allowance recorded	0	3,242
Interest Income Recognized
With no related allowance recorded	0	20
With an allowance recorded	0	841
Cash Basis Interest Income
With no related allowance recorded	0	28
With an allowance recorded	$ 0	$ 838

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