Segment Reporting (Schedule Of Underwriting Results For Operating Segments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Premiums earned	$ 1,494,005	$ 1,270,454
Incurred losses and LAE	1,029,513	796,096
Commission and brokerage	323,104	288,218
Other underwriting expenses	101,208	78,382
Underwriting gain (loss)	40,180	107,758
U.S. Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premiums	1,308,194	1,153,111
Net written premiums	1,114,235	975,999
Premiums earned	1,007,034	897,278
Incurred losses and LAE	682,707	553,714
Commission and brokerage	260,901	236,965
Other underwriting expenses	29,847	24,056
Underwriting gain (loss)	33,579	82,543
Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premiums	666,771	531,771
Net written premiums	524,474	416,244
Premiums earned	486,970	373,176
Incurred losses and LAE	346,805	242,382
Commission and brokerage	62,203	51,253
Other underwriting expenses	71,361	54,326
Underwriting gain (loss)	$ 6,601	$ 25,215