Reserve For Losses And Loss Expenses (Schedule Of Reserve For Losses And Loss Expenses) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Insurance Loss Reserves [Abstract]
Outstanding loss reserves	$ 1,707,409		$ 1,514,051
Reserves for losses incurred but not reported	4,729,170		4,367,114
Reserve for losses and loss expenses	$ 6,436,579	$ 6,363,948	$ 5,881,165	$ 6,052,263	$ 5,935,678	$ 5,766,529