CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue
Net earned premium	$ 16.3	$ 29.2	$ 30.1	$ 54.5
Ceding commission income	10.6	0.4	19.6	0.4
Net investment income	0.2	0.2	0.4	1.1
Commission and other income	1.1	0.1	1.6	0.1
Total revenue	28.2	29.9	51.7	56.1
Expense
Loss and loss adjustment expense, net	13.0	20.5	29.5	38.7
Other insurance expense	5.2	4.0	10.0	7.3
Sales and marketing	33.1	16.1	62.2	35.3
Technology development	14.0	4.2	21.1	7.7
General and administrative	15.8	5.8	29.9	24.0
Total expense	81.1	50.6	152.7	113.0
Loss before income taxes	(52.9)	(20.7)	(101.0)	(56.9)
Income tax expense	2.7	0.3	3.6	0.6
Net loss	(55.6)	(21.0)	(104.6)	(57.5)
Other comprehensive income, net of tax
Unrealized (loss) gain on investments	(0.2)	0.2	(0.1)	0.2
Foreign currency translation adjustment	0.3	0.0	1.0	0.0
Comprehensive loss	$ (55.5)	$ (20.8)	$ (103.7)	$ (57.3)
Earnings Per Share [Abstract]
Net loss per share attributable to common stockholders—basic (usd per share)	$ (0.90)	$ (1.77)	$ (1.72)	$ (4.89)
Net loss per share attributable to common stockholders—diluted (usd per share)	$ (0.90)	$ (1.77)	$ (1.72)	$ (4.89)
Weighted average common shares outstanding—basic (shares)	61,444,958	11,891,979	60,643,764	11,750,198
Weighted average common shares outstanding—diluted (shares)	61,444,958	11,891,979	60,643,764	11,750,198