DERIVATIVE INSTRUMENTS (Schedule of Derivative Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	$ 1,343	$ 8,237
Derivative liability fair value	17,601	14,522
Not Designated as Hedging Instruments \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	1,343	8,237
Not Designated as Hedging Instruments \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	17,601	14,522
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	152,963	79,336
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	517	262
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	425	531
Not Designated as Hedging Instruments \| Relating to investment portfolio \| Interest rate swaps
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	0	150,000
Not Designated as Hedging Instruments \| Relating to investment portfolio \| Interest rate swaps \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	0	0
Not Designated as Hedging Instruments \| Relating to investment portfolio \| Interest rate swaps \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	0	1,116
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	531,864	737,419
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	826	7,975
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	7,040	2,576
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	85,000	85,000
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	$ 10,136	$ 10,299

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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Fair value, after the effects of master netting arrangements, of a financial liability or 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 liabilities not subject to a master netting arrangement and not elected to be offset.

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