Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023		Dec. 31, 2022	Dec. 31, 2021
Effective Tax Rate Reconciliation [Line Items]
Statutory tax rate	21.00%		21.00%	21.00%
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent	(0.40%)		(0.30%)	(0.20%)
Dividends received exclusion	(1.00%)		(1.30%)	(0.70%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Meals and Entertainment, Percent	0.30%		0.20%	0.10%
Other items - net	0.00%		0.30%	0.00%
Effective tax rates (credit)	19.90%		19.90%	20.20%
Deferred Tax Assets [Abstract]
Deferred Tax Assets, losses, claims, and settlement expenses	$ 214.9		$ 218.6	$ 214.2
Deferred Tax Assets, Pension and deferred compensation plans	23.8		22.6	42.4
Deferred Tax Assets, Impairment losses on investments	9.5		0.0	0.0
Deferred Tax Assets, Net operating loss carryforward	5.5		7.6	9.6
Deferred Tax Assets, AMT credit carryforward	9.0		9.0	9.0
Deferred Tax Asset - Operating Lease Right of Use Asset	46.4		46.7	49.7
Deferred Tax Assets, Other temporary differences	16.3		17.1	12.3
Total deferred tax assets	325.4		321.6	337.5
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilties, Unearned premium reserves	46.3		63.3	61.0
Deferred Tax Liabilities, Deferred policy acquisition costs	82.8		76.0	68.5
Deferred Tax Liabilities, Amortization of fixed maturity securities	14.6		6.8	5.2
Deferred Tax Liabilities, Net unrealized investment gains	214.4		141.3	372.6
Deferred Tax Liabilities, Title plants and records	2.8		2.8	2.8
Deferred tax Liabilities - TCJA Discounted reserves transition adjustment	6.7		10.3	13.8
Deferred Tax Liability - Operating Lease Liability	40.9		41.9	45.8
Deferred Tax Liabilities, Other temporary differences	22.5		20.1	17.2
Deferred Tax Liabilities, Gross	431.0		362.5	586.9
Deferred Tax Liabilities, Net	(105.6)	[1]	$ (40.9)	$ (249.5)
Operating loss carryforwards	26.4
Disposal Group, Not Discontinued Operations
Deferred Tax Assets [Abstract]
Total deferred tax assets	0.3
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Gross	0.1
Maximum [Member]
Deferred Tax Liabilities [Abstract]
Operating loss carryforwards	$ 9.8

[1] RFIG Run-off deferred tax assets of $0.3 and deferred tax liabilities of $0.1 have been reclassified as held-for-sale as of December 31, 2023. See Note 2 for further discussion