RESERVE FOR LOSSES AND LOSS EXPENSES (DETAILS 8) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Claims Development [Line Items]
Net outstanding liabilities	$ 7,426,671
Reinsurance recoverable on unpaid claims	2,276,109
Gross outstanding liabilities	9,702,780
Unallocated claims adjustment expenses	144,375
Foreign exchange and other	(59,988)
(Ceded)/assumed reserves related to retroactive transactions	(89,340)
Reserve for losses and loss expenses	9,697,827	$ 9,646,285	$ 9,596,797	$ 9,582,140
Insurance [Member]
Claims Development [Line Items]
Net outstanding liabilities	3,212,646
Reinsurance recoverable on unpaid claims	2,193,329
Gross outstanding liabilities	5,405,975
Insurance [Member] | Property and Other Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	582,637
Reinsurance recoverable on unpaid claims	169,707
Gross outstanding liabilities	752,344
Insurance [Member] | Marine Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	253,308
Reinsurance recoverable on unpaid claims	180,996
Gross outstanding liabilities	434,304
Insurance [Member] | Aviation Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	54,550
Reinsurance recoverable on unpaid claims	6,384
Gross outstanding liabilities	60,934
Insurance [Member] | Credit and Political Risk Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	51,637
Reinsurance recoverable on unpaid claims	154
Gross outstanding liabilities	51,791
Insurance [Member] | Professional Lines Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,717,559
Reinsurance recoverable on unpaid claims	998,873
Gross outstanding liabilities	2,716,432
Insurance [Member] | Liability Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	552,955
Reinsurance recoverable on unpaid claims	837,215
Gross outstanding liabilities	1,390,170
Reinsurance [Member]
Claims Development [Line Items]
Net outstanding liabilities	4,214,025
Reinsurance recoverable on unpaid claims	82,780
Gross outstanding liabilities	4,296,805
Reinsurance [Member] | Property and Other Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	823,463
Reinsurance recoverable on unpaid claims	55,637
Gross outstanding liabilities	879,100
Reinsurance [Member] | Credit and Surety Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	356,668
Reinsurance recoverable on unpaid claims	1,916
Gross outstanding liabilities	358,584
Reinsurance [Member] | Professional Lines Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,154,464
Reinsurance recoverable on unpaid claims	8,353
Gross outstanding liabilities	1,162,817
Reinsurance [Member] | Motor Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	811,156
Reinsurance recoverable on unpaid claims	0
Gross outstanding liabilities	811,156
Reinsurance [Member] | Liability Reserve Class [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,068,274
Reinsurance recoverable on unpaid claims	16,874
Gross outstanding liabilities	$ 1,085,148