Reinsurance Reinsurance (Schedule Of Ceded Credit Risk by Reinsurer) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	$ 848,609
Residual market pools	367,070
Ceded credit risk, total amount	1,215,679
Munich Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	163,420
Swiss Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	72,690
Transatlantic Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	64,619
Partner Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	60,769
Berkshire Hathaway [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	56,042
Axis Capital [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	54,121
Lloyds of London [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	52,859
Ace Group [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	43,463
Hannover Re Group [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	33,262
Arch Capital Group [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	22,984
Other Reinsurers Less Than $20,000 [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	$ 224,380