Geographical Breakdown of Gross Written Premium (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) segment	Mar. 31, 2022 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 164.0	$ 110.6
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	$ 45.5	$ 27.1
California | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	27.70%	24.50%
Texas
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 26.1	$ 20.2
Texas | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	15.90%	18.30%
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 18.4	$ 14.8
New York | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	11.20%	13.40%
New Jersey
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 8.6	$ 5.3
New Jersey | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	5.20%	4.80%
Illinois
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 7.1	$ 4.4
Illinois | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.30%	4.00%
Washington
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 6.1	$ 2.0
Washington | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	3.70%	1.80%
Georgia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 4.9	$ 4.4
Georgia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	3.00%	4.00%
Oregon
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 4.5	$ 2.0
Oregon | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.80%	1.90%
Colorado
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 4.3	$ 3.0
Colorado | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.60%	2.80%
Arizona
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 4.1	$ 2.2
Arizona | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.50%	2.00%
All other
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 34.4	$ 25.2
All other | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	21.10%	22.50%