RESERVE FOR LOSSES AND LOSS EXPENSES (DETAILS) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Reconciliation of Beginning and Ending Gross Unpaid Losses and Loss Expenses
Gross reserve for losses and loss expenses, beginning of period			$ 8,425,045	$ 7,032,375
Less reinsurance recoverable on unpaid losses, beginning of period			(1,736,823)	(1,540,633)
Net reserve for unpaid losses and loss expenses, beginning of period			6,688,222	5,491,742
Net incurred losses and loss expenses related to:
Current year			1,098,168	1,686,013
Prior years	(74,612)	(51,550)	(119,840)	(101,254)
Net incurred losses and loss expenses			978,328	1,584,759
Net paid losses and loss expenses related to:
Current year			(90,041)	(84,858)
Prior years			(731,363)	(472,454)
Net paid losses and loss expenses			(821,404)	(557,312)
Foreign exchange and other			(10,129)	126,056
Net reserve for unpaid losses and loss expenses, end of period	6,835,017	6,645,245	6,835,017	6,645,245
Reinsurance recoverable on unpaid losses, end of period	1,765,634	1,757,367	1,765,634	1,757,367
Gross reserve for losses and loss expenses, end of period	$ 8,600,651	$ 8,402,612	$ 8,600,651	$ 8,402,612