Long-Duration Insurance Contracts - Amounts Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	$ 60.1	$ 60.1	$ 177.0	$ 178.3
Interest expense	18.8	18.9	56.5	56.8
Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	7.1	7.2	20.9	20.5
Interest expense	3.1	3.0	9.1	8.8
Term Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	11.1	11.7	33.3	33.9
Interest expense	1.4	1.2	4.0	3.6
Experience Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	8.5	8.1	23.9	24.2
Interest expense	10.7	10.9	32.3	32.8
Limited Pay Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	1.8	2.2	5.2	5.5
Interest expense	0.7	0.6	2.1	1.9
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	30.3	30.0	90.7	89.7
Interest expense	1.9	2.1	5.8	6.4
Life Contingent SPIA Retirement Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	1.3	0.9	3.0	4.5
Interest expense	$ 1.0	$ 1.1	$ 3.2	$ 3.3