Segment Reporting (Schedule Of Underwriting Results For Operating Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Premiums earned	$ 1,851,364	$ 1,615,457	$ 5,314,819	$ 4,648,422
Incurred losses and LAE	1,653,019	1,277,851	4,102,721	3,283,196
Commission and brokerage	388,847	322,404	1,125,549	1,001,207
Other underwriting expenses	109,512	109,366	329,238	304,705
Underwriting gain (loss)	(300,014)	(94,164)	(242,688)	59,314
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premiums	1,693,027	1,473,266	4,552,364	3,906,355
Net written premiums	1,461,238	1,296,107	3,961,280	3,403,090
Premiums earned	1,280,181	1,153,740	3,689,508	3,223,608
Incurred losses and LAE	1,207,528	936,904	2,917,285	2,250,270
Commission and brokerage	319,707	265,095	935,252	818,282
Other underwriting expenses	32,049	35,697	101,337	92,143
Underwriting gain (loss)	(279,103)	(83,956)	(264,366)	62,913
Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premiums	830,688	591,695	2,421,716	1,971,818
Net written premiums	608,248	429,594	1,801,884	1,462,869
Premiums earned	571,183	461,717	1,625,311	1,424,814
Incurred losses and LAE	445,491	340,947	1,185,435	1,032,926
Commission and brokerage	69,139	57,309	190,296	182,925
Other underwriting expenses	77,464	73,669	227,901	212,562
Underwriting gain (loss)	$ (20,911)	$ (10,208)	$ 21,678	$ (3,599)