Catastrophe Reinsurance - Catastrophe Reinsurance Premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	$ 42.7	$ 36.1	$ 31.2
Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	32.0	30.3	26.7
Specialty Property & Casualty Insurance | Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	8.9	7.0	4.8
Preferred Property & Casualty Insurance | Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	22.5	22.0	20.7
Life & Health Insurance | Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Ceded earned premiums	$ 0.6	$ 1.3	$ 1.2