MORTGAGE LOANS - Impaired Loans (Details) - Commercial mortgage loans - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Recorded Investment
With no related allowance recorded, recorded investment	$ 0	$ 0
With an allowance recorded, recorded investment	5,684	0
Unpaid Principal Balance
With no related allowance recorded, unpaid principal balance	0	0
With an allowance recorded, unpaid principal balance	5,309	0
Related Allowance
With an allowance recorded, related allowance	1,296	0
Average Recorded Investment
With no related allowance recorded, average recorded investment	0	0
With an allowance recorded, average recorded investment	1,895	0
Interest Income Recognized
With no related allowance recorded, interest income recognized	0	0
With an allowance recorded, interest income recognized	267	0
Cash Basis Interest Income
With no related allowance recorded, cash basis interest income	0	0
With an allowance recorded, recorded investment	$ 293	$ 0

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-Publisher FASB
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