DERIVATIVE INSTRUMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	$ 6,912	$ 16,897
Derivative Liability Fair Value	13,276	15,576
Other Assets [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	6,912	16,897
Other Liabilities [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	13,276	15,576
Investment Portfolio [Member] \| Foreign Exchange Forward Contracts [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Notional Amount	160,998	195,979
Investment Portfolio [Member] \| Foreign Exchange Forward Contracts [Member] \| Other Assets [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	0	12,331
Investment Portfolio [Member] \| Foreign Exchange Forward Contracts [Member] \| Other Liabilities [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	748	87
Investment Portfolio [Member] \| Interest Rate Swap [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Notional Amount	180,000	0
Investment Portfolio [Member] \| Interest Rate Swap [Member] \| Other Assets [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	0	0
Investment Portfolio [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	0	0
Underwriting Portfolio [Member] \| Foreign Exchange Forward Contracts [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Notional Amount	479,347	492,899
Underwriting Portfolio [Member] \| Foreign Exchange Forward Contracts [Member] \| Other Assets [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	6,912	2,034
Underwriting Portfolio [Member] \| Foreign Exchange Forward Contracts [Member] \| Other Liabilities [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	319	8,989
Underwriting Portfolio [Member] \| Weather Related Derivative [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Notional Amount	3,050	67,957
Underwriting Portfolio [Member] \| Weather Related Derivative [Member] \| Other Assets [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	0	2,532
Underwriting Portfolio [Member] \| Weather Related Derivative [Member] \| Other Liabilities [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	74	6,500
Underwriting Portfolio [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Notional Amount	0	0
Underwriting Portfolio [Member] \| Commodity Contract [Member] \| Other Assets [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	0	0
Underwriting Portfolio [Member] \| Commodity Contract [Member] \| Other Liabilities [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	0	0
Underwriting Portfolio [Member] \| Other Underwriting-related Contracts [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Notional Amount	75,000	0
Underwriting Portfolio [Member] \| Other Underwriting-related Contracts [Member] \| Other Assets [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Asset Fair Value	0	0
Underwriting Portfolio [Member] \| Other Underwriting-related Contracts [Member] \| Other Liabilities [Member] \| Not Designated as Hedging Instruments [Member]
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative Liability Fair Value	$ 12,135	$ 0

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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