DERIVATIVE INSTRUMENTS (Schedule of Derivative Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	$ 3,254	$ 18,875
Derivative liability fair value	28,167	11,486
Not Designated as Hedging Instruments \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	3,254	18,875
Not Designated as Hedging Instruments \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	28,167	11,486
Not Designated as Hedging Instruments \| Relating to investment portfolio: \| Foreign exchange forward contracts
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	313,081	105,781
Not Designated as Hedging Instruments \| Relating to investment portfolio: \| Foreign exchange forward contracts \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	3,026	2
Not Designated as Hedging Instruments \| Relating to investment portfolio: \| Foreign exchange forward contracts \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	198	2,364
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Foreign exchange forward contracts
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	1,159,353	1,197,012
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Foreign exchange forward contracts \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	228	18,873
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Foreign exchange forward contracts \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	19,507	0
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Other underwriting-related contracts
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	75,000	75,000
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Other underwriting-related contracts \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	0	0
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Other underwriting-related contracts \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	$ 8,462	$ 9,122

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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