Long-Duration Insurance Contracts - Amounts Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	$ 59.2	$ 59.1
Interest expense	18.9	19.0
Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	6.9	6.6
Interest expense	3.0	2.9
Term Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	11.2	10.8
Interest expense	1.3	1.2
Experience Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	7.7	8.2
Interest expense	10.8	11.0
Limited Pay Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	1.8	1.6
Interest expense	0.7	0.6
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	30.4	29.7
Interest expense	2.0	2.2
Life Contingent SPIA Retirement Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	1.2	2.2
Interest expense	$ 1.1	$ 1.1