Reserve For Losses And Loss Expenses (Schedule Of Reserve For Losses And Loss Expenses) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Insurance Loss Reserves [Abstract]
Outstanding loss reserves	$ 1,585,900		$ 1,520,867
Reserves for losses incurred but not reported	4,466,363		4,245,662
Reserve for losses and loss expenses	$ 6,052,263	$ 5,935,678	$ 5,766,529	$ 5,780,781	$ 5,696,865	$ 5,645,549