Income Taxes - Reconciliation of Effective Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Expected federal tax on income	$ (2.5)	$ 36.7	$ 33.5
Add (deduct) tax effects of:
Tax-exempt interest	(3.3)	(3.9)	(4.2)
Dividend received deduction	(3.2)	(2.2)	(1.5)
Goodwill impairment	0.0	0.0	0.2
CARES Act net operating loss carryback	0.0	0.0	(2.8)
Employee share-based compensation	(0.5)	(1.3)	(0.5)
Contingent consideration	(0.3)	0.0	0.0
Compensation deduction limitation	0.7	1.5	0.7
Research and development reserve	(0.4)	0.0	0.2
Prior year adjustments	0.1	0.1	(0.2)
Other, net	0.1	1.2	0.9
Total income tax expense (benefit)	$ (9.3)	$ 32.1	$ 26.3