Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Effects of Reinsurance [Line Items]
Direct premiums written	$ 2,909,657	$ 2,852,425
Direct premiums earned	2,934,728	2,901,920
Assumed premiums written	1,308,573	1,087,974
Assumed premiums earned	682,351	516,213
Ceded premiums written	(1,907,939)	(1,708,362)
Ceded premiums earned	(1,527,705)	(1,290,506)
Net premiums written	2,310,291	2,232,037
Net premiums earned	2,089,374	2,127,627
Underwriting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	2,135,972	2,107,467
Direct premiums earned	2,195,483	2,198,238
Assumed premiums written	729,042	668,699
Assumed premiums earned	438,045	392,942
Ceded premiums written	(554,725)	(543,956)
Ceded premiums earned	(544,156)	(463,380)
Net premiums written	2,310,289	2,232,210
Net premiums earned	2,089,372	2,127,800
Fronting
Effects of Reinsurance [Line Items]
Direct premiums written	773,685	744,958
Direct premiums earned	739,245	703,682
Assumed premiums written	579,531	419,275
Assumed premiums earned	244,306	123,271
Ceded premiums written	(1,353,214)	(1,164,406)
Ceded premiums earned	(983,549)	(827,126)
Net premiums written	2	(173)
Net premiums earned	$ 2	$ (173)

Amount of earned premiums assumed from other entities.

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