RESERVE FOR LOSSES AND LOSS EXPENSES (DETAILS 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Additional Information Related to Net Incurred Losses [Line Items]
Current year net loss and loss expenses	$ 2,353,631	$ 2,340,868	$ 2,932,513
Net favorable (adverse) prior year reserve development	219,436	244,840	257,461
Short Tail Lines Insurance And Reinsurance Business [Member]
Additional Information Related to Net Incurred Losses [Line Items]
Net favorable (adverse) prior year reserve development	162,000	186,000	178,000
Liability Reinsurance Business [Member]
Additional Information Related to Net Incurred Losses [Line Items]
Net favorable (adverse) prior year reserve development	85,000
Professional Lines Insurance And Reinsurance Business [Member]
Additional Information Related to Net Incurred Losses [Line Items]
Net favorable (adverse) prior year reserve development	(29,000)	54,000	105,000
Professional Lines Insurance Business [Member]
Additional Information Related to Net Incurred Losses [Line Items]
Net favorable (adverse) prior year reserve development	(51,000)
Catastrophe and Weather-related Events [Member]
Additional Information Related to Net Incurred Losses [Line Items]
Current year net loss and loss expenses	$ 201,000	$ 438,000	$ 944,000