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	$ 2,036,814	$ 1,732,697
Incurred losses and LAE	1,430,840	1,048,550
Commission and brokerage	448,522	389,474
Other underwriting expenses	128,860	98,985
Underwriting gain (loss)	28,592	195,688
U.S. Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	1,777,771	1,532,051
Net written premiums	1,613,094	1,394,553
Premiums earned	1,485,221	1,307,519
Incurred losses and LAE	1,020,642	772,198
Commission and brokerage	370,356	322,637
Other underwriting expenses	44,139	35,769
Underwriting gain (loss)	50,084	176,915
Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	793,100	595,057
Net written premiums	588,385	457,145
Premiums earned	551,593	425,178
Incurred losses and LAE	410,198	276,352
Commission and brokerage	78,166	66,837
Other underwriting expenses	84,721	63,216
Underwriting gain (loss)	$ (21,492)	$ 18,773