Segment Information - Schedule of gross written premium by state (Details) $ in Millions	3 Months Ended
	Mar. 31, 2025 USD ($) employee	Mar. 31, 2024 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 254.2	$ 205.6
Number of reportable segments | employee	1
Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	100.00%	100.00%
California
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 60.4	$ 55.3
California | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	23.80%	26.90%
Texas
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 32.5	$ 30.0
Texas | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	12.80%	14.60%
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 25.9	$ 21.0
New York | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	10.20%	10.20%
Washington
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 13.0	$ 8.0
Washington | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	5.10%	3.90%
New Jersey
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 11.7	$ 9.7
New Jersey | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.60%	4.70%
Illinois
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 11.6	$ 9.7
Illinois | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.60%	4.70%
Pennsylvania
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 7.0	$ 5.1
Pennsylvania | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.80%	2.50%
Colorado
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 6.8	$ 5.9
Colorado | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.70%	2.90%
Georgia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 6.5	$ 5.6
Georgia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.60%	2.70%
Florida
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 6.3	$ 3.1
Florida | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.50%	1.50%
All other
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 63.1	$ 49.1
All other | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	24.60%	23.90%
US
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 244.8	$ 202.5
US | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	96.30%	98.50%
Europe and UK
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 9.4	$ 3.1
Europe and UK | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	3.70%	1.50%