Geographical Breakdown of Gross Written Premium (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 555.7	$ 375.7	$ 214.4
Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	100.00%	100.00%	100.00%
California
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 142.0	$ 93.9	$ 49.8
California | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	25.60%	25.00%	23.20%
Texas
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 91.3	$ 72.5	$ 47.8
Texas | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	16.40%	19.30%	22.30%
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 66.0	$ 47.3	$ 26.7
New York | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	11.90%	12.60%	12.50%
New Jersey
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 28.3	$ 16.7	$ 8.6
New Jersey | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	5.10%	4.40%	4.00%
Illinois
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 26.3	$ 15.7	$ 9.8
Illinois | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.70%	4.20%	4.60%
Georgia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 19.8	$ 16.5	$ 11.6
Georgia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	3.60%	4.40%	5.40%
Washington
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 15.8	$ 5.4	$ 1.1
Washington | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.80%	1.40%	0.50%
Colorado
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 15.8	$ 9.2	$ 4.2
Colorado | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.80%	2.40%	2.00%
Pennsylvania
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 14.4	$ 9.7	$ 5.1
Pennsylvania | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.60%	2.60%	2.40%
Virginia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 13.0	$ 8.1	$ 3.9
Virginia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.30%	2.20%	1.80%
All others
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 123.0	$ 80.7	$ 45.8
All others | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	22.20%	21.50%	21.30%