QUARTERLY FINANCIAL INFORMATION (unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Quarterly Financial Information [Line Items]
Total revenues	$ 577.7	$ 545.7	$ 523.7	$ 513.8	$ 394.1	$ 388.7	$ 353.1	$ 296.7	$ 2,160.9	$ 1,432.6	$ 882.8
Operating expenses:
Medical claims expense									1,645.0	1,109.0	617.8
Cost of care									437.8	293.7	187.5
Sales and marketing	43.8	44.1	42.6	33.8	38.9	30.5	25.9	24.1	164.3	119.4	64.2
Corporate, general and administrative	79.5	81.7	94.9	88.7	82.4	77.0	74.2	73.1	344.8	306.7	185.6
Depreciation and amortization	9.9	9.1	8.4	7.8	6.1	4.5	3.9	3.3
Total operating expenses	709.9	675.9	636.4	604.9	535.6	498.1	452.4	360.5
Loss from operations	(132.2)	(130.2)	(112.7)	(91.1)	(141.5)	(109.4)	(99.3)	(63.8)	(466.2)	(414.0)	(183.5)
Other (expense)/income:
Interest expense, net	(1.4)	0.0	(0.5)	(0.6)	(0.7)	(0.6)	(1.0)	(0.2)	(2.5)	(2.5)	(8.7)
Other	(0.5)	(0.2)	(35.1)	(5.0)	0.0	0.0	0.0	0.0	(40.8)	0.0	0.1
Total other (expense)	(1.9)	(0.2)	(35.6)	(5.6)	(0.7)	(0.6)	(1.0)	(0.2)	(43.3)	(2.5)	(8.6)
Income before income taxes and non-controlling interests	(134.1)	(130.4)	(148.3)	(96.7)	(142.2)	(110.0)	(100.3)	(64.0)	(509.5)	(416.5)	(192.1)
Provision (benefit) for income taxes	0.2	0.0	0.0	0.0	(1.9)	0.0	0.0	0.0	0.2	(1.9)	0.0
Net loss	(134.3)	(130.4)	(148.3)	(96.7)	(140.3)	(110.0)	(100.3)	(64.0)	(509.7)	(414.6)	(192.1)
Net loss attributable to non-controlling interests	(1.4)	0.3	0.8	(0.2)	(1.7)	(0.6)	(2.3)	(0.6)	(0.5)	(5.2)	(4.1)
Net loss attributable to the Company	$ (132.9)	$ (130.7)	$ (149.1)	$ (96.5)	$ (138.6)	$ (109.4)	$ (98.0)	$ (63.4)	$ (509.2)	$ (409.4)	$ (188.0)
Net loss per share – diluted (in dollars per share)	$ (0.56)	$ (0.56)	$ (0.66)	$ (0.43)	$ (0.62)	$ (0.49)	$ (0.44)	$ (0.29)	$ (2.21)	$ (1.84)	$ (0.55)
Net loss per share – basic (in dollars per share)	$ (0.56)	$ (0.56)	$ (0.66)	$ (0.43)	$ (0.62)	$ (0.49)	$ (0.44)	$ (0.29)	$ (2.21)	$ (1.84)	$ (0.55)
Medical Claims Expenses
Operating expenses:
Medical claims expense	$ 446.6	$ 427.4	$ 391.6	$ 379.4	$ 318.1	$ 309.8	$ 281.4	$ 199.7
Cost of Care
Operating expenses:
Cost of care	130.1	113.6	98.9	95.2	90.1	76.3	67.0	60.3
Capitated revenue
Schedule Of Quarterly Financial Information [Line Items]
Total revenues	565.8	537.9	516.1	506.1	382.4	376.7	346.7	291.2	$ 2,125.9	$ 1,397.0	$ 851.3
Other revenue
Schedule Of Quarterly Financial Information [Line Items]
Total revenues	$ 11.9	$ 7.8	$ 7.6	$ 7.7	$ 11.7	$ 12.0	$ 6.4	$ 5.5	$ 35.0	$ 35.6	$ 31.5