DERIVATIVE INSTRUMENTS (Other Underwriting-related Risks) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Unrealized and Realized Gains (Losses) Recognized in Earnings for Derivatives Not Designated As Hedges [Line Items]
Unrealized and realized gains (losses) recognized in earnings for derivatives not designated as hedges	$ (797)	$ (246)	$ (24,443)	$ (7,973)
Relating to investment portfolio: | Foreign exchange forward contracts | Net investment gains (losses)
Unrealized and Realized Gains (Losses) Recognized in Earnings for Derivatives Not Designated As Hedges [Line Items]
Unrealized and realized gains (losses) recognized in earnings for derivatives not designated as hedges	(537)	154	1,212	3,316
Relating to underwriting portfolio: | Foreign exchange forward contracts | Foreign exchange gains (losses)
Unrealized and Realized Gains (Losses) Recognized in Earnings for Derivatives Not Designated As Hedges [Line Items]
Unrealized and realized gains (losses) recognized in earnings for derivatives not designated as hedges	(604)	(870)	(26,660)	(1,559)
Relating to underwriting portfolio: | Other underwriting-related contracts | Other insurance related income (losses)
Unrealized and Realized Gains (Losses) Recognized in Earnings for Derivatives Not Designated As Hedges [Line Items]
Unrealized and realized gains (losses) recognized in earnings for derivatives not designated as hedges	$ 344	$ 470	$ 1,005	$ (9,730)