Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Loss, LAE and unearned premium reserves, net	$ 197.6	$ 185.6
Investments, net	97.2	144.3
Employee benefit plans	7.3	8.4
Other	9.2	7.3
Total deferred tax assets	311.3	345.6
Deferred acquisition costs	130.4	127.0
Software capitalization	7.6	19.4
Total deferred tax liabilities	138.0	146.4
Net deferred tax asset	$ 173.3	$ 199.2