Geographical Breakdown of Gross Written Premium (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Gross Written Premium [Line Items]
Amount	$ 117.1	$ 99.2
Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	100.00%	100.00%
Texas
Gross Written Premium [Line Items]
Amount	$ 33.9	$ 33.0
Texas | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	28.90%	33.30%
California
Gross Written Premium [Line Items]
Amount	$ 22.1	$ 18.9
California | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	18.90%	19.10%
Florida
Gross Written Premium [Line Items]
Amount	$ 6.8	$ 5.8
Florida | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	5.80%	5.80%
Georgia
Gross Written Premium [Line Items]
Amount	$ 6.1	$ 4.1
Georgia | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	5.20%	4.10%
Illinois
Gross Written Premium [Line Items]
Amount	$ 3.5	$ 3.1
Illinois | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	3.00%	3.10%
Colorado
Gross Written Premium [Line Items]
Amount	$ 3.2	$ 2.5
Colorado | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	2.70%	2.50%
Missouri
Gross Written Premium [Line Items]
Amount	$ 3.0	$ 2.4
Missouri | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	2.60%	2.40%
Arizona
Gross Written Premium [Line Items]
Amount	$ 3.1	$ 2.4
Arizona | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	2.60%	2.40%
Ohio
Gross Written Premium [Line Items]
Amount	$ 2.6	$ 2.0
Ohio | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	2.20%	2.00%
New Jersey
Gross Written Premium [Line Items]
Amount	$ 2.6	$ 2.2
New Jersey | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	2.20%	2.20%
Other
Gross Written Premium [Line Items]
Amount	$ 30.2	$ 22.8
Other | Geographic Concentration Risk | Gross written premium
Gross Written Premium [Line Items]
Concentration risk, percentage	25.80%	23.00%