Reinsurance and Catastrophes - Effects of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Gross Amount
Premiums written and contract deposits, Gross Amount									$ 1,583.6	$ 1,499.0		$ 1,373.6
Premiums and contract charges earned, Gross Amount									1,097.7	1,046.7		912.4
Benefits, claims and settlement expenses, Gross Amount									803.6	772.5		592.3
Ceded to Other Companies
Premiums written and contract deposits, Ceded to Other Companies									67.9	62.9		23.1
Premiums and contract charges earned, Ceded to Other Companies									76.3	72.0		33.3
Benefits, claims and settlement expenses, Ceded to Other Companies									45.7	43.5		7.8
Assumed from Other Companies
Premiums written and contract deposits, Assumed from Other Companies									36.9	53.0		9.4
Premiums and contract charges earned, Assumed from Other Companies									35.7	53.0		9.7
Benefits, claims and settlement expenses, Assumed from Other Companies									11.2	18.0		6.2
Net Amount
Premiums written and contract deposits, Net Amount	$ 358.2	$ 372.7	$ 359.9	$ 346.2	$ 314.0	$ 346.2	$ 334.2	$ 304.4	1,552.6	1,489.1		1,359.9
Premiums and contract charges earned, Net Amount	$ 259.1	$ 257.4	$ 255.4	$ 255.8	$ 210.6	$ 225.2	$ 225.6	$ 227.4	1,057.1	1,027.7		888.8
Benefits, claims and settlement expenses									$ 769.1	$ 747.0	[1]	$ 590.7	[1]

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements