Stock-based Compensation - Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 14.8	$ 13.9	$ 30.2	$ 28.0
Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	9.3	11.9	20.3	24.0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4.9	2.0	9.3	4.0
Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0.6	0.0	0.6	0.0
Loss and loss adjustment expense, net
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0.7	0.6	1.4	1.2
Other insurance expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0.5	0.5	1.0	0.8
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1.5	1.7	2.7	3.2
Technology development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	6.3	5.8	13.0	11.2
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5.8	$ 5.3	$ 12.1	$ 11.6