Other Reinsurance (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) employees director	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$ 86.5	$ 99.6
Ceded earned premiums	32.7	42.7	$ 36.1
Assumed earned premiums	29.7	26.3	34.7
Catastrophe Reinsurance
Effects of Reinsurance [Line Items]
Ceded earned premiums	16.3	32.0	30.3
Non-Catastrophe Reinsurance
Effects of Reinsurance [Line Items]
Assumed earned premiums	42.9	41.4	56.7
Property and Liability Insurance
Effects of Reinsurance [Line Items]
Reinsurance recoverables	27.8	39.6	41.9	$ 50.1
Ceded earned premiums	17.8	38.0	34.9
Assumed earned premiums	29.2	24.3	29.6
Short duration policies
Effects of Reinsurance [Line Items]
Reinsurance recoverables	34.1	47.3
Long-duration policies
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$ 52.4	52.3
Capitol County Mutual Fire Insurance Company
Effects of Reinsurance [Line Items]
Number of employee board members | employees	5
Number of board of director members | director	5
Old Reliable Casualty Company
Effects of Reinsurance [Line Items]
Number of employee board members | employees	9
Number of board of director members | director	9
Capitol County Mutual Fire Insurance Company
Effects of Reinsurance [Line Items]
Assumed earned premiums	$ 10.4	11.9	17.3
Capitol County Mutual Fire Insurance Company | Trinity
Effects of Reinsurance [Line Items]
Percentage of written business assumed	100.00%
Old Reliable Casualty Company
Effects of Reinsurance [Line Items]
Assumed earned premiums	$ 2.7	$ 3.2	$ 4.7
Old Reliable Casualty Company | Trinity
Effects of Reinsurance [Line Items]
Percentage of written business assumed	100.00%