Reserve For Losses And Loss Expenses (Schedule Of Reserve For Losses And Loss Expenses) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Insurance Loss Reserves [Abstract]
Outstanding loss reserves	$ 1,514,051	$ 1,520,867
Reserves for losses incurred but not reported	4,367,114	4,245,662
Reserve for losses and loss expenses	$ 5,881,165	$ 5,766,529	$ 5,645,549	$ 5,225,143