INVESTMENTS - Allowance for Credit Losses, Unrealized Losses on Securities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Securities in unrealized loss positions
Allowance for credit losses	$ 878		$ 0
Debt securities
Securities in unrealized loss positions
Number of debt securities for which there is an allowance for credit losses | security	39
Allowance for credit losses	$ 900
Number of debt securities in an unrealized loss position for which an allowance for credit losses has not been recorded | security	381
Number of unrealized loss positions | security	420
Number of securities in unrealized loss positions for 12 months or longer | security	30
Unrealized loss	$ 28,500
Unrealized losses as percentage of fixed income portfolio cost basis	1.50%
Unrealized losses relative to total invested assets (as a percent)	1.20%
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Recognized in Earnings		$ 0
Equity securities
Securities in unrealized loss positions
Unrealized gains (losses) on equity securities still held	$ (115,200)	$ 41,900