Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of period	$ 2,584,910	$ 2,226,430
Reinsurance recoverables on unpaid losses	25,322	41,377
Net reserves, beginning of period	2,559,588	2,185,053
Incurred losses and loss adjustment expenses related to:
Current year	2,683,219	2,386,233
Prior years	(32,138)	49,942
Total incurred losses and loss adjustment expenses	2,651,081	2,436,175
Loss and loss adjustment expense payments related to:
Current year	1,461,077	1,267,535
Prior years	1,052,386	945,371
Total payments	2,513,463	2,212,906
Net reserves, end of period	2,697,206	2,408,322
Reinsurance recoverables on unpaid losses, end of period	26,570	24,412
Gross reserves, end of period	$ 2,723,776	$ 2,432,734