Reinsurance - Impact of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Premium written:
Direct	$ 730.9	$ 555.6	$ 375.7
Assumed	7.5	0.1	0.0
Ceded	(389.1)	(333.1)	(273.4)
Net premium written	349.3	222.6	102.3
Premium earned:
Direct	667.2	490.5	292.0
Assumed	5.1	0.0	0.0
Ceded	(357.1)	(318.1)	(215.0)
Net premium earned	315.2	172.4	77.0
Loss and LAE incurred:
Direct	563.4	441.0	264.1
Assumed	6.0	0.0	0.0
Ceded	(289.0)	(273.7)	(192.2)
Net loss and LAE incurred	$ 280.4	$ 167.3	$ 71.9

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