CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income
Beginning balance (in shares) at Dec. 31, 2021		61,660,996
Beginning balance at Dec. 31, 2021	$ 988.2	$ 0.0	$ 1,553.5	$ (561.9)	$ (3.4)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		97,743
Exercise of stock options and distribution of restricted stock units	0.6		0.6
Stock-based compensation	14.1		14.1
Net loss	(74.8)			(74.8)
Other comprehensive income (loss)	(15.4)				(15.4)
Ending balance (in shares) at Mar. 31, 2022		61,758,739
Ending balance at Mar. 31, 2022	912.7	$ 0.0	1,568.2	(636.7)	(18.8)
Beginning balance (in shares) at Dec. 31, 2021		61,660,996
Beginning balance at Dec. 31, 2021	988.2	$ 0.0	1,553.5	(561.9)	(3.4)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Issuance of common stock from acquisition of Metromile (Note 5) (in shares)		6,901,934
Issuance of common stock from acquisition of Metromile (Note 5)	137.7		137.7
Net loss	(234.1)
Ending balance (in shares) at Sep. 30, 2022		69,120,346
Ending balance at Sep. 30, 2022	906.8	$ 0.0	1,738.1	(796.0)	(35.3)
Beginning balance (in shares) at Mar. 31, 2022		61,758,739
Beginning balance at Mar. 31, 2022	912.7	$ 0.0	1,568.2	(636.7)	(18.8)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		108,838
Exercise of stock options and distribution of restricted stock units	0.4		0.4
Stock-based compensation	13.9		13.9
Net loss	(67.9)			(67.9)
Other comprehensive income (loss)	(10.0)				(10.0)
Ending balance (in shares) at Jun. 30, 2022		61,867,577
Ending balance at Jun. 30, 2022	849.1	$ 0.0	1,582.5	(704.6)	(28.8)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		350,835
Exercise of stock options and distribution of restricted stock units	2.3		2.3
Stock-based compensation	15.6		15.6
Net loss	(91.4)			(91.4)
Other comprehensive income (loss)	(6.5)				(6.5)
Ending balance (in shares) at Sep. 30, 2022		69,120,346
Ending balance at Sep. 30, 2022	$ 906.8	$ 0.0	1,738.1	(796.0)	(35.3)
Beginning balance (in shares) at Dec. 31, 2022	69,275,030	69,275,030
Beginning balance at Dec. 31, 2022	$ 866.8	$ 0.0	1,754.1	(859.7)	(27.6)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		174,318
Exercise of stock options and distribution of restricted stock units	0.1		0.1
Stock-based compensation	15.4		15.4
Net loss	(65.8)			(65.8)
Other comprehensive income (loss)	5.3				5.3
Ending balance (in shares) at Mar. 31, 2023		69,449,348
Ending balance at Mar. 31, 2023	$ 821.8	$ 0.0	1,769.6	(925.5)	(22.3)
Beginning balance (in shares) at Dec. 31, 2022	69,275,030	69,275,030
Beginning balance at Dec. 31, 2022	$ 866.8	$ 0.0	1,754.1	(859.7)	(27.6)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Net loss	$ (194.5)
Ending balance (in shares) at Sep. 30, 2023	69,909,356	69,909,356
Ending balance at Sep. 30, 2023	$ 726.9	$ 0.0	1,800.2	(1,054.2)	(19.1)
Beginning balance (in shares) at Mar. 31, 2023		69,449,348
Beginning balance at Mar. 31, 2023	821.8	$ 0.0	1,769.6	(925.5)	(22.3)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		218,828
Exercise of stock options and distribution of restricted stock units	0.3		0.3
Stock-based compensation	14.8		14.8
Net loss	(67.2)			(67.2)
Other comprehensive income (loss)	1.3				1.3
Ending balance (in shares) at Jun. 30, 2023		69,668,176
Ending balance at Jun. 30, 2023	771.0	$ 0.0	1,784.7	(992.7)	(21.0)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		241,180
Exercise of stock options and distribution of restricted stock units	0.1		0.1
Stock-based compensation	15.4		15.4
Net loss	(61.5)			(61.5)
Other comprehensive income (loss)	$ 1.9				1.9
Ending balance (in shares) at Sep. 30, 2023	69,909,356	69,909,356
Ending balance at Sep. 30, 2023	$ 726.9	$ 0.0	$ 1,800.2	$ (1,054.2)	$ (19.1)