Geographical Breakdown of Gross Written Premium (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Gross Written Premium [Line Items]
Amount	$ 244.8	$ 161.8	$ 434.2	$ 278.9
Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	100.00%	100.00%	100.00%	100.00%
Texas
Gross Written Premium [Line Items]
Amount	$ 44.2	$ 43.1	$ 83.8	$ 77.0
Texas | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	18.10%	26.60%	19.30%	27.60%
California
Gross Written Premium [Line Items]
Amount	$ 43.2	$ 31.2	$ 76.0	$ 53.3
California | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	17.70%	19.30%	17.50%	19.10%
Florida
Gross Written Premium [Line Items]
Amount	$ 38.0	$ 15.9	$ 59.5	$ 22.7
Florida | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	15.50%	9.80%	13.70%	8.10%
Georgia
Gross Written Premium [Line Items]
Amount	$ 13.0	$ 7.5	$ 22.2	$ 13.6
Georgia | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	5.30%	4.60%	5.10%	4.90%
Colorado
Gross Written Premium [Line Items]
Amount	$ 6.7	$ 4.0	$ 12.5	$ 7.2
Colorado | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	2.70%	2.50%	2.90%	2.60%
Arizona
Gross Written Premium [Line Items]
Amount	$ 4.6	$ 3.3	$ 9.1	$ 6.4
Arizona | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	1.90%	2.10%	2.10%	2.30%
Illinois
Gross Written Premium [Line Items]
Amount	$ 7.3	$ 5.9	$ 12.4	$ 9.4
Illinois | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	3.00%	3.60%	2.90%	3.40%
New Jersey
Gross Written Premium [Line Items]
Amount	$ 4.0	$ 1.9	$ 8.3	$ 4.5
New Jersey | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	1.60%	1.20%	1.90%	1.60%
Ohio
Gross Written Premium [Line Items]
Amount	$ 4.2	$ 3.8	$ 7.9	$ 6.4
Ohio | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	1.70%	2.40%	1.80%	2.30%
Missouri
Gross Written Premium [Line Items]
Amount	$ 3.9	$ 3.6	$ 7.5	$ 6.6
Missouri | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	1.60%	2.20%	1.70%	2.40%
Other
Gross Written Premium [Line Items]
Amount	$ 75.7	$ 41.6	$ 135.0	$ 71.8
Other | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	30.90%	25.70%	31.10%	25.70%