Reinsurance Reinsurance (Schedule Of Ceded Credit Risk by Reinsurer) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	$ 1,045,800
Residual market pools	404,548
Ceded credit risk, total amount	1,450,348
Munich Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	166,910
Lloyds of London [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	127,430
Swiss Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	81,167
Transatlantic Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	79,835
Partner Re [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	71,785
Axis Capital [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	60,140
Berkshire Hathaway [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	54,152
Ace Group [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	46,020
Hannover Re Group [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	32,763
Poseidon Re Ltd [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	30,016
Everest Re (Member) [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	25,915
Arch Capital Group [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	25,636
Validus Holding LTD [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	23,727
Other Reinsurers Less Than $20,000 [Member]
Ceded Credit Risk [Line Items]
Ceded credit risk, claims receivable	$ 220,304