MORTGAGE LOANS - Delinquent Loans (Details) - Commercial mortgage loans $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Delinquent loans
Commercial mortgage loans | $	$ 814	$ 1,817
Number of delinquent commercial mortgage loans | loan	1	2
30-59 Days Delinquent
Delinquent loans
Commercial mortgage loans | $	$ 814	$ 1,817
Number of delinquent commercial mortgage loans | loan	1	2
60-89 Days Delinquent
Delinquent loans
Commercial mortgage loans | $	$ 0	$ 0
Number of delinquent commercial mortgage loans | loan	0	0
Greater than 90 Days Delinquent
Delinquent loans
Commercial mortgage loans | $	$ 0	$ 0
Number of delinquent commercial mortgage loans | loan	0	0