Summary of Significant Accounting Policies - Effects of Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums Written
Direct	$ 3,907,500	$ 3,654,200	$ 3,774,600
Net	3,860,000	3,610,000	3,730,000
Premiums Earned
Direct	3,793,664	3,603,780	3,655,233
Ceded	(65,017)	(56,212)	(56,725)
Assumed	13,301	8,067	910
Net	3,741,948	3,555,635	3,599,418
Property & Casualty
Premiums Written
Direct	3,877,476	3,624,965	3,742,627
Ceded	(65,521)	(50,630)	(43,785)
Assumed	13,361	8,012	919
Net	3,825,316	3,582,347	3,699,761
Premiums Earned
Direct	3,764,626	3,574,898	3,626,857
Ceded	(65,017)	(56,212)	(56,725)
Assumed	13,301	8,067	910
Net	$ 3,712,910	$ 3,526,753	$ 3,571,042