Summary of Significant Accounting Policies - Effects of Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Written
Direct	$ 4,048,500	$ 3,907,500	$ 3,654,200
Net	3,980,000	3,860,000	3,610,000
Premiums Earned
Direct	4,022,611	3,793,664	3,603,780
Ceded	(80,950)	(65,017)	(56,212)
Assumed	10,821	13,301	8,067
Net	3,952,482	3,741,948	3,555,635
Property & Casualty
Premiums Written
Direct	4,018,057	3,877,476	3,624,965
Ceded	(81,256)	(65,521)	(50,630)
Assumed	10,743	13,361	8,012
Net	3,947,544	3,825,316	3,582,347
Premiums Earned
Direct	3,993,771	3,764,626	3,574,898
Ceded	(80,950)	(65,017)	(56,212)
Assumed	10,821	13,301	8,067
Net	$ 3,923,642	$ 3,712,910	$ 3,526,753