INVESTMENTS - OTTI recognized in earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	$ 9,733	$ 14,493	$ 26,210
Non-U.S. government
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	4,697	8,187	3,557
Corporate debt
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	4,995	6,306	20,093
Non-Agency CMBS
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	41	0	0
Fixed maturities
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	9,733	14,493	23,650
Exchange-traded funds
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	0	0	2,560
Equity securities
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net [Line Items]
Total OTTI recognized in net income	$ 0	$ 0	$ 2,560