INVESTMENTS - Schedule of Held-to-maturity, Allowance for Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Allowance for credit losses:
Beginning balance	$ 6
Ending balance	5
State and political subdivisions
Allowance for credit losses:
Beginning balance	6	$ 0
Provision for credit losses	(1)	0
Charge-offs, net	0	0
Ending balance	5	8
State and political subdivisions | Cumulative change in accounting principle
Allowance for credit losses:
Beginning balance	$ 0	$ 8