INVESTMENTS - Allowance for Credit Losses, Unrealized Losses on Securities (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Securities in unrealized loss positions
Allowance for credit losses	$ 985		$ 985		$ 0
Debt securities
Securities in unrealized loss positions
Number of debt securities for which there is an allowance for credit losses | security	36		36
Allowance for credit losses	$ 1,000		$ 1,000
Number of debt securities in an unrealized loss position for which an allowance for credit losses has not been recorded | security	249		249
Number of unrealized loss positions | security	285		285
Number of securities in unrealized loss positions for 12 months or longer | security	32		32
Unrealized loss	$ 7,700		$ 7,700
Unrealized losses as percentage of fixed income portfolio cost basis	0.40%		0.40%
Unrealized losses relative to total invested assets (as a percent)	0.30%		0.30%
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	$ 72,400	$ 12,900	$ (42,900)	$ 54,800