CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (236.9)	$ (297.8)	$ (241.3)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	20.0	12.2	3.7
Stock-based compensation	59.9	59.3	44.1
Amortization of premium (discount) on bonds	(2.6)	6.7	(4.2)
Provision for bad debt	8.1	8.7	6.2
Asset impairment charge	3.7	0.0	0.0
Changes in operating assets and liabilities:
Premium receivable	(50.5)	(43.8)	(47.2)
Reinsurance recoverable	18.4	(52.6)	(40.8)
Prepaid reinsurance premium	(31.8)	(14.9)	(58.3)
Deferred acquisition costs	(1.9)	(0.8)	(2.7)
Other assets	8.9	(7.0)	(38.6)
Unpaid losses and loss adjustment expenses	6.1	74.0	51.6
Unearned premium	65.7	65.1	83.9
Trade payables	(0.5)	(0.7)	(0.4)
Funds held for reinsurance treaties	(7.2)	32.9	41.0
Deferred ceding commission	1.7	3.2	14.1
Ceded premium payable	4.8	(12.4)	5.7
Other liabilities and accrued expenses	15.0	4.9	38.6
Net cash used in operating activities	(119.1)	(163.0)	(144.6)
Cash flows from investing activities:
Acquisition of business, net of cash acquired	0.0	98.8	0.0
Proceeds from short-term investments sold or matured	143.5	224.5	20.2
Proceeds from bonds sold or matured	349.6	138.0	27.2
Cost of short-term investments acquired	(71.5)	(136.7)	(130.8)
Cost of bonds acquired	(323.7)	(133.4)	(712.0)
Purchases of property and equipment	(9.2)	(10.1)	(9.4)
Net cash provided by (used in) investing activities	88.7	181.1	(804.8)
Cash flows from financing activities:
Proceeds from borrowings under financing agreement	19.1	0.0	0.0
Payment on borrowings under financing agreement	(4.2)	0.0	0.0
Proceeds from Initial Public Offering and Follow-on Offering, net of underwriting discounts and commissions and offering costs	0.0	0.0	640.3
Proceeds from stock exercises	0.5	3.6	9.3
Net cash provided by financing activities	15.4	3.6	649.6
Effect of exchange rate changes on cash, cash equivalents and restricted cash	0.0	(5.8)	(1.0)
Net increase (decrease) in cash, cash equivalents and restricted cash	(15.0)	15.9	(300.8)
Cash, cash equivalents and restricted cash at beginning of year	286.5	270.6	571.4
Cash, cash equivalents and restricted cash at end of year	271.5	286.5	270.6
Supplemental disclosure of cash flow information:
Cash paid for income taxes	0.7	3.4	3.2
Cash paid for interest expense on borrowings under financing agreement	0.3	0.0	0.0
Non-cash transactions:
Warrants assumed from acquisition of Metromile	$ 0.0	$ 0.3	$ 0.0