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
	Mar. 31, 2014	Mar. 31, 2013
Insurance Loss Reserves [Abstract]
Gross liability at beginning of year	$ 5,766,529	$ 5,645,549
Reinsurance recoverable at beginning of year	(1,234,504)	(1,141,110)
Net liability at beginning of year	4,532,025	4,504,439
Net losses incurred related to:
Current year	324,147	299,248
Prior years	(48,861)	(44,070)
Total incurred	275,286	255,178
Net paid losses related to:
Current year	3,743	3,581
Prior years	228,594	241,121
Total paid	232,337	244,702
Foreign exchange revaluation	1,299	(5,198)
Net liability at end of year	4,576,273	4,509,717
Reinsurance recoverable at end of year	1,280,525	1,163,503
Gross liability at end of year	$ 5,856,798	$ 5,673,220