Segment Information - Schedule of Segment Reporting Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 737.9	$ 526.5	$ 429.8
less: Loss and loss adjustment expenses, net	347.0	277.0	280.4
Other insurance expense	93.7	76.8	59.2
Sales and marketing	224.4	166.3	101.9
Advertising expenses	187.3	121.5	55.2
Technology development	93.9	85.8	88.8
Income tax expense (benefit)	4.6	(1.7)	7.1
Net loss	(165.5)	(202.2)	(236.9)
Gain (loss) on termination of lease	2.3	0.0	0.0
Gain (loss) from litigation settlement	1.0
San Francisco
Revenues from External Customers and Long-Lived Assets [Line Items]
Gain (loss) on termination of lease	2.3
Impairment loss on subleased right-of-use asset			3.7
Federal | CARES Act, ERC Program
Revenues from External Customers and Long-Lived Assets [Line Items]
Tax credits	11.7
Metromile
Revenues from External Customers and Long-Lived Assets [Line Items]
Liabilities assumed			3.0
Reportable Segment
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	737.9	526.5	429.8
less: Loss and loss adjustment expenses, net	347.0	277.0	280.4
Other insurance expense	93.7	76.8	59.2
Sales and marketing	37.1	44.8	46.7
Advertising expenses	187.3	121.5	55.2
Technology development	93.9	85.8	88.8
General and administrative	122.3	98.0	102.2
Interest expense	17.3	6.2	0.4
Depreciation and amortization	15.2	20.0	20.0
Other expenses	(15.0)	0.3	6.7
Income tax expense (benefit)	4.6	(1.7)	7.1
Net loss	$ (165.5)	(202.2)	$ (236.9)
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Impairment loss on subleased right-of-use asset		$ 0.3