Reinsurance (Reinsurance Financial Information) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2010
Reinsurance Disclosures [Abstract]
Written premiums, direct	$ 1,201,019,000	$ 1,076,847,000
Written premiums, assumed	200,507,000	193,011,000
Written premiums, ceded	(198,000,000)	(186,555,000)
Total net premiums written	1,203,526,000	1,083,303,000
Earned premiums, direct	1,103,956,000	972,525,000
Earned premiums, assumed	179,518,000	161,870,000
Earned premiums, ceded	(183,823,000)	(151,898,000)
Net premiums earned	1,099,651,000	982,497,000
Ceded losses incurred	85,277,000	114,825,000
Uncollectible reinsurance	$ 3,000,000		$ 3,000,000