CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (202.2)	$ (236.9)	$ (297.8)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	20.0	20.0	12.2
Stock-based compensation	64.5	59.9	59.3
Amortization of premium (discount) on bonds	(6.1)	(2.6)	6.7
Provision for bad debt	11.0	8.1	8.7
Asset impairment charge	0.3	3.7	0.0
Changes in operating assets and liabilities:
Premium receivable	(90.2)	(50.5)	(43.8)
Reinsurance recoverable	(32.0)	18.4	(52.6)
Prepaid reinsurance premium	(57.3)	(31.8)	(14.9)
Deferred acquisition costs	(3.4)	(1.9)	(0.8)
Other assets	21.2	8.9	(7.0)
Unpaid losses and loss adjustment expenses	35.8	6.1	74.0
Unearned premium	101.3	65.7	65.1
Trade payables	3.9	(0.5)	(0.7)
Funds held for reinsurance treaties	90.8	(7.2)	32.9
Deferred ceding commission	24.2	1.7	3.2
Ceded premium payable	0.6	4.8	(12.4)
Other liabilities and accrued expenses	6.2	15.0	4.9
Net cash used in operating activities	(11.4)	(119.1)	(163.0)
Cash flows from investing activities:
Acquisition of business, net of cash acquired	0.0	0.0	98.8
Proceeds from short-term investments sold or matured	77.5	143.5	224.5
Proceeds from bonds sold or matured	336.3	349.6	138.0
Cost of short-term investments acquired	(58.1)	(71.5)	(136.7)
Cost of bonds acquired	(305.7)	(323.7)	(133.4)
Purchases of property and equipment	(9.4)	(9.2)	(10.1)
Net cash provided by investing activities	40.6	88.7	181.1
Cash flows from financing activities:
Proceeds from borrowings under financing agreement	96.1	19.1	0.0
Payment on borrowings under financing agreement	(27.7)	(4.2)	0.0
Proceeds from stock exercises	19.3	0.5	3.6
Net cash provided by financing activities	87.7	15.4	3.6
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(2.7)	0.0	(5.8)
Net increase (decrease) in cash, cash equivalents and restricted cash	114.2	(15.0)	15.9
Cash, cash equivalents and restricted cash at beginning of year	271.5	286.5	270.6
Cash, cash equivalents and restricted cash at end of year	385.7	271.5	286.5
Supplemental disclosure of cash flow information:
Cash paid for income taxes	2.5	0.7	3.4
Cash paid for interest expense on borrowings under financing agreement	5.0	0.3	0.0
Non-cash transactions:
Warrants assumed from acquisition of Metromile	$ 0.0	$ 0.0	$ 0.3