Reinsurance (Schedule Of Ceded Credit Risk by Reinsurer) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	$ 1,503,441	$ 1,533,103
Credit Risk Reinsurers, Subtotal, Excluding Residual Market Pools [Member]
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	997,879
Munich Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	141,489
Lloyds of London
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	109,976
Swiss Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	101,308
Alleghany Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	97,300
Partner Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	70,756
Axis Capital
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	63,352
Berkshire Hathaway
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	48,804
Ace Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	44,215
Hannover Re Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	43,207
Everest Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	41,749
Arch Capital Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	23,453
Other Reinsurers
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	212,270
Residual Market Pools
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	$ 505,562