Reserve For Losses And Loss Expenses (Schedule Of Reconciliation Of Unpaid Losses And Loss Expenses) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Insurance Loss Reserves [Abstract]
Gross liability at beginning of year	$ 5,935,678	$ 5,696,865	$ 5,766,529	$ 5,645,549
Reinsurance recoverable at beginning of year	(1,301,742)	(1,179,525)	(1,234,504)	(1,141,110)
Net liability at beginning of year	4,633,936	4,517,340	4,532,025	4,504,439
Net losses incurred related to:
Current year	382,970	338,420	1,067,111	961,224
Prior years	(46,880)	(61,450)	(140,880)	(153,948)
Total incurred	336,090	276,970	926,231	807,276
Net paid losses related to:
Current year	53,596	30,399	80,401	54,983
Prior years	202,626	213,252	666,555	696,137
Total paid	256,222	243,651	746,956	751,120
Foreign exchange revaluation	(10,550)	4,088	(8,046)	(5,848)
Net liability at end of year	4,703,254	4,554,747	4,703,254	4,554,747
Reinsurance recoverable at end of year	1,349,009	1,226,034	1,349,009	1,226,034
Gross liability at end of year	$ 6,052,263	$ 5,780,781	$ 6,052,263	$ 5,780,781