Geographical Breakdown of Gross Written Premium (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 205.6	$ 164.0
Number of reportable segments | segment	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	$ 55.3	$ 45.5
California | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	26.90%	27.70%
Texas
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 30.0	$ 26.1
Texas | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	14.60%	15.90%
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 21.0	$ 18.4
New York | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	10.20%	11.20%
Illinois
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 9.7	$ 7.1
Illinois | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.70%	4.30%
New Jersey
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 9.7	$ 8.6
New Jersey | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.70%	5.20%
Washington
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 8.0	$ 6.1
Washington | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	3.90%	3.70%
Colorado
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 5.9	$ 4.3
Colorado | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.90%	2.60%
Georgia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 5.6	$ 4.9
Georgia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.70%	3.00%
Pennsylvania
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 5.1	$ 4.1
Pennsylvania | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.50%	2.50%
Arizona
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 5.0	$ 4.1
Arizona | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.40%	2.50%
All other
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 50.3	$ 34.8
All other | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	24.50%	21.40%