Reinsurance (Reinsurance Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reinsurance Disclosures [Abstract]
Written premiums, Direct	$ 10,695,138	$ 9,531,050	$ 7,874,050
Written premiums, Assumed	1,213,914	1,169,084	973,597
Written premiums, Ceded	(1,904,982)	(1,837,267)	(1,585,210)
Total net premiums written	10,004,070	8,862,867	7,262,437
Earned premiums, Direct	10,217,891	8,825,568	7,489,470
Earned premiums, Assumed	1,226,801	1,085,804	941,321
Earned premiums, Ceded	(1,883,263)	(1,805,341)	(1,499,948)
Net premiums earned	9,561,429	8,106,031	6,930,843
Ceded losses and loss expenses incurred	1,269,338	1,236,960	955,630
Ceded commission earned	477,437	449,739	358,253
Uncollectible reinsurance	$ 8,064	$ 7,713	$ 7,801