Reinsurance and Catastrophes - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Gross Amount
Premiums written and contract deposits, Gross Amount	$ 1,495.2	$ 1,370.1	$ 1,369.9
Premiums and contract charges earned, Gross Amount	1,048.0	913.2	949.6
Benefits, claims and settlement expenses, Gross Amount	787.2	619.3	475.7
Ceded to Other Companies
Premiums written and contract deposits, Ceded to Other Companies	62.9	23.1	20.4
Premiums and contract charges earned, Ceded to Other Companies	72.0	33.3	28.8
Benefits, claims and settlement expenses, Ceded to Other Companies	43.6	7.8	(86.2)
Assumed from Other Companies
Premiums written and contract deposits, Assumed from Other Companies	53.0	9.4	9.8
Premiums and contract charges earned, Assumed from Other Companies	53.0	9.7	9.9
Benefits, claims and settlement expenses, Assumed from Other Companies	18.0	6.2	7.0
Net Amount
Premiums written and contract deposits, Net Amount	1,485.3	1,356.4	1,359.3
Premiums and contract charges earned, Net Amount	1,029.0	889.6	930.7
Benefits, claims and settlement expenses	$ 761.6	$ 617.7	$ 568.9