DERIVATIVE INSTRUMENTS (Schedule of Derivative Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	$ 863	$ 8,237
Derivative liability fair value	12,948	14,522
Other assets \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	863	8,237
Other liabilities \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	12,948	14,522
Investment Portfolio \| Foreign exchange forward contracts \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	189,811	79,336
Investment Portfolio \| Foreign exchange forward contracts \| Other assets \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	147	262
Investment Portfolio \| Foreign exchange forward contracts \| Other liabilities \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	1,074	531
Investment Portfolio \| Interest rate swaps \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	0	150,000
Investment Portfolio \| Interest rate swaps \| Other assets \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	0	0
Investment Portfolio \| Interest rate swaps \| Other liabilities \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	0	1,116
Underwriting Portfolio \| Foreign exchange forward contracts \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	534,811	737,419
Underwriting Portfolio \| Foreign exchange forward contracts \| Other assets \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	716	7,975
Underwriting Portfolio \| Foreign exchange forward contracts \| Other liabilities \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	1,612	2,576
Underwriting Portfolio \| Other underwriting-related contracts \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	85,000	85,000
Underwriting Portfolio \| Other underwriting-related contracts \| Other assets \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	0	0
Underwriting Portfolio \| Other underwriting-related contracts \| Other liabilities \| Not Designated as Hedging Instruments
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	$ 10,262	$ 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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