Reinsurance and Catastrophes - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Gross Amount
Premiums written and contract deposits, Gross Amount	$ 1,370.1	$ 1,369.9	$ 1,337.8
Premiums and contract charges earned, Gross Amount	913.2	949.6	917.6
Benefits, claims and settlement expenses, Gross Amount	619.3	475.7	633.9
Ceded to Other Companies
Premiums written and contract deposits, Ceded to Other Companies	23.1	20.4	23.9
Premiums and contract charges earned, Ceded to Other Companies	33.3	28.8	30.4
Benefits, claims and settlement expenses, Ceded to Other Companies	7.8	(86.2)	56.3
Assumed from Other Companies
Premiums written and contract deposits, Assumed from Other Companies	9.4	9.8	10.6
Premiums and contract charges earned, Assumed from Other Companies	9.7	9.9	10.8
Benefits, claims and settlement expenses, Assumed from Other Companies	6.2	7.0	7.5
Net Amount
Premiums written and contract deposits, Net Amount	1,356.4	1,359.3	1,324.5
Premiums and contract charges earned, Net Amount	889.6	930.7	898.0
Benefits, claims and settlement expenses	$ 617.7	$ 568.9	$ 585.1