Reinsurance and Catastrophes - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Gross Amount
Premiums written and contract deposits, Gross Amount	$ 1,650.9	$ 1,583.6	$ 1,499.0
Premiums and contract charges earned, Gross Amount	1,188.8	1,097.7	1,046.7
Benefits, claims and settlement expenses, Gross Amount	748.3	803.6	772.5
Ceded to Other Companies
Premiums written and contract deposits, Ceded to Other Companies	72.0	67.9	62.9
Premiums and contract charges earned, Ceded to Other Companies	70.9	76.3	72.0
Benefits, claims and settlement expenses, Ceded to Other Companies	43.0	45.7	43.5
Assumed from Other Companies
Premiums written and contract deposits, Assumed from Other Companies	28.8	36.9	53.0
Premiums and contract charges earned, Assumed from Other Companies	28.1	35.7	53.0
Benefits, claims and settlement expenses, Assumed from Other Companies	39.7	11.2	18.0
Net Amount
Premiums written and contract deposits, Net Amount	1,607.7	1,552.6	1,489.1
Premiums and contract charges earned, Net Amount	1,146.0	1,057.1	1,027.7
Benefits, claims and settlement expenses	$ 745.0	$ 769.1	$ 747.0	[1]

[1] Recast for the adoption of ASU 2018-12.