Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net deferred tax assets and liabilities [Abstract]
Total deferred tax assets	$ 32,331	$ 38,443
Total deferred tax liabilities	(71,743)	(98,485)
Net deferred tax liability	(39,412)	(60,042)
Components of net deferred tax asset [Abstract]
Unearned premium reserves	19,116	23,163
Benefit plans	(21,360)	(13,977)
Loss reserves	4,034	3,542
Unrealized appreciation in investments	(39,883)	(72,341)
Deferred Policy Acquisition Cost	(4,551)	(4,528)
Deferred compensation	6,118	6,776
Other, net	(2,886)	(2,677)
Components of provisions for (benefit from) income taxes [Abstract]
Current Federal	161,055	85,574	$ 162,911
Deferred Federal	4,392	28,244	11,860
Other	1,347	(648)	(557)
Provision for income taxes	$ 166,794	$ 113,170	$ 174,214
Reconciliation of effective income tax rate [Abstract]
Federal statutory income tax rate (in hundredths)	21.00%	21.00%	21.00%
Tax exempt municipal bond interest (in hundredths)	(0.60%)	(0.90%)	(0.60%)
Other, net (in hundredths)	0.40%	0.10%	0.10%
Effective income tax provision rate (in hundredths)	20.80%	20.20%	20.50%
Income taxes paid	$ 155,300	$ 79,600	$ 158,300
Amount of tax and loss bonds held	426,300
Unrecognized tax benefits	$ 0	$ 0