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Reinsurance (List of direct, assumed and ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums Written:
Direct premiums written	$ 3,656,537	$ 3,204,512	$ 3,084,451
Assumed	22,664	24,288	24,339
Ceded premiums written	(489,488)	(455,708)	(429,366)
Net	3,189,713	2,773,092	2,679,424
Direct premiums written	3,656,537	3,204,512	3,084,451
Premiums Earned:
Direct	3,472,715	3,108,687	2,993,157
Assumed	21,550	25,010	24,399
Ceded premiums earned	(477,012)	(451,883)	(420,385)
Total Net Premiums Earned	3,017,253	2,681,814	2,597,171
Loss and loss expense incurred:
Direct	2,096,512	1,822,034	1,714,880
Assumed	13,813	17,201	22,879
Ceded loss and loss expense	(296,341)	(203,412)	(186,268)
Net	$ 1,813,984	$ 1,635,823	$ 1,551,491
Increase in DPW from Prior Year	14.00%	4.00%
Return audit and midterm endorsement premium [Member] | COVID-19 [Member]
Premiums Written:
Direct premiums written	$ 75,000
Direct premiums written	75,000
Commercial & Personal Automobile [Member] | COVID-19 [Member]
Premiums Written:
Direct premiums written	19,700
Direct premiums written	$ 19,700

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