REINSURANCE (DETAILS) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Premiums written:
Gross									$ 4,096,153,000	$ 3,750,536,000	$ 3,587,295,000
Ceded									(676,719,000)	(602,996,000)	(770,866,000)
Net									3,419,434,000	3,147,540,000	2,816,429,000
Premiums Earned:
Gross									3,973,956,000	3,632,177,000	3,540,298,000
Ceded									(658,995,000)	(684,767,000)	(748,534,000)
Net	846,753,000	839,992,000	840,014,000	788,201,000	757,318,000	758,873,000	735,027,000	696,192,000	3,314,961,000	2,947,410,000	2,791,764,000
Reinsurance recoverable on unpaid and paid losses
Ceded losses and loss expenses									450,000,000	425,000,000	319,000,000
Provision for unrecoverable reinsurance	$ 18,000,000				$ 17,000,000				$ 18,000,000	$ 17,000,000
Percentage of gross reinsurance recoverables collectable with reinsurers rated A- or better by AM Best	98.60%				97.90%				98.60%	97.90%