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RESERVE FOR LOSSES AND LOSS EXPENSES (DETAILS 2) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Reconciliation of Beginning and Ending Gross Unpaid Losses and Loss Expenses [Roll Forward]      
Gross reserve for losses and loss expenses, beginning of period $ 7,032,375 $ 6,564,133 $ 6,244,783
Less reinsurance recoverable on unpaid losses, beginning of period (1,540,633) (1,381,058) (1,314,551)
Net reserve for losses and loss expenses, beginning of period 5,491,742 5,183,075 4,930,232
Net incurred losses and loss expenses related to:      
Current year 2,932,513 1,990,187 1,847,044
Prior years (257,461) (313,055) (423,172)
Net incurred losses 2,675,052 1,677,132 1,423,872
Net paid losses and loss expenses related to:      
Current year (509,075) (300,293) (271,011)
Prior years (953,035) (1,042,890) (982,036)
Net paid losses (1,462,110) (1,343,183) (1,253,047)
Foreign exchange and other (16,462) (25,282) 82,018
Net reserve for losses and loss expenses, end of period 6,688,222 5,491,742 5,183,075
Reinsurance recoverable on unpaid losses, end of period 1,736,823 1,540,633 1,381,058
Gross reserve for losses and loss expenses, end of period $ 8,425,045 $ 7,032,375 $ 6,564,133