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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Insurance Loss Reserves [Abstract]
Gross liability at beginning of year	$ 5,856,798	$ 5,673,220	$ 5,766,529	$ 5,645,549
Reinsurance recoverable at beginning of year	(1,280,525)	(1,163,503)	(1,234,504)	(1,141,110)
Net liability at beginning of year	4,576,273	4,509,717	4,532,025	4,504,439
Net losses incurred related to:
Current year	359,994	323,556	684,141	622,804
Prior years	(45,139)	(48,428)	(94,000)	(92,498)
Total incurred	314,855	275,128	590,141	530,306
Net paid losses related to:
Current year	23,065	21,003	26,808	24,584
Prior years	235,335	241,764	463,929	482,885
Total paid	258,400	262,767	490,737	507,469
Foreign exchange revaluation	1,208	(4,738)	2,507	(9,936)
Net liability at end of year	4,633,936	4,517,340	4,633,936	4,517,340
Reinsurance recoverable at end of year	1,301,742	1,179,525	1,301,742	1,179,525
Gross liability at end of year	$ 5,935,678	$ 5,696,865	$ 5,935,678	$ 5,696,865