Geographical Breakdown of Gross Written Premium (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	1
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 110.6	$ 75.8
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	$ 27.1	$ 19.2
California | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	24.50%	25.30%
Texas
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 20.2	$ 15.0
Texas | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	18.30%	19.80%
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 14.8	$ 10.0
New York | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	13.40%	13.20%
New Jersey
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 5.3	$ 3.1
New Jersey | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.80%	4.10%
Illinois
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 4.4	$ 3.0
Illinois | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.00%	4.00%
Georgia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 4.4	$ 3.7
Georgia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	4.00%	4.90%
Colorado
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 3.0	$ 1.4
Colorado | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.70%	1.80%
Pennsylvania
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 2.7	$ 1.8
Pennsylvania | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.40%	2.40%
Virginia
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 2.4	$ 1.5
Virginia | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.20%	2.00%
Maryland
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 2.2	$ 1.6
Maryland | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	2.00%	2.10%
All other
Revenues from External Customers and Long-Lived Assets [Line Items]
Amount	$ 24.1	$ 15.5
All other | Gross written premium | Geographic Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
% of GWP	21.70%	20.40%