Segment Information - Schedule of Gross Written Premium by State (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 380.0	$ 284.5	$ 723.9	$ 538.7
Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	100.00%	100.00%	100.00%	100.00%
California
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 77.9	$ 61.3	$ 151.6	$ 121.7
California | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	20.50%	21.50%	20.90%	22.60%
Texas
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 52.1	$ 38.8	$ 92.8	$ 71.3
Texas | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	13.70%	13.60%	12.80%	13.20%
New York
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 34.0	$ 27.0	$ 67.3	$ 52.9
New York | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	8.90%	9.50%	9.30%	9.80%
Washington
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 19.2	$ 14.5	$ 37.3	$ 27.5
Washington | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	5.10%	5.10%	5.20%	5.10%
Illinois
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 16.8	$ 14.1	$ 30.7	$ 25.7
Illinois | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	4.40%	5.00%	4.20%	4.80%
New Jersey
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 15.5	$ 12.8	$ 29.9	$ 24.5
New Jersey | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	4.10%	4.50%	4.10%	4.50%
Colorado
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 16.1	$ 10.7	$ 29.0	$ 17.5
Colorado | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	4.20%	3.80%	4.00%	3.20%
Florida
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 13.0	$ 8.2	$ 24.2	$ 14.5
Florida | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	3.40%	2.90%	3.30%	2.70%
Arizona
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 10.5	$ 7.3	$ 20.4	$ 13.5
Arizona | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	2.80%	2.60%	2.80%	2.50%
Pennsylvania
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 10.8	$ 8.3	$ 20.3	$ 15.3
Pennsylvania | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	2.80%	2.90%	2.80%	2.80%
All other
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 98.6	$ 71.9	$ 188.9	$ 135.3
All other | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	26.00%	25.30%	26.20%	25.30%
US
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 364.5	$ 274.9	$ 692.4	$ 519.7
US | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	95.90%	96.60%	95.60%	96.50%
Europe and UK
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Amount	$ 15.5	$ 9.6	$ 31.5	$ 19.0
Europe and UK | Gross written premium | Geographic Concentration Risk
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
% of GWP	4.10%	3.40%	4.40%	3.50%