Reinsurance Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Effects of Reinsurance [Line Items]
Net losses and loss adjustment expenses	$ 1,290,612	$ 1,404,325	$ 3,810,934	$ 3,765,215
Underwriting [Member]
Effects of Reinsurance [Line Items]
Gross losses and loss adjustment expenses	1,710,637	1,684,389	4,982,304	4,552,926
Ceded losses and loss adjustment expenses	(419,194)	(278,945)	(1,170,585)	(786,876)
Net losses and loss adjustment expenses	$ 1,291,443	$ 1,405,444	$ 3,811,719	$ 3,766,050