EARNINGS (LOSS) PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net income (loss) attributable to Oscar Health, Inc.	$ (54,596)	$ (65,398)	$ 178,979	$ (120,698)
Effect of convertible senior notes	0	0	17,459	0
Net income (loss) available to Oscar Health, Inc. common shareholders	$ (54,596)	$ (65,398)	$ 196,438	$ (120,698)
Denominator:
Weighted average shares of common stock outstanding, basic (in shares)	243,106,000	223,099,000	237,759,000	219,827,000
Common stock equivalents (in shares)	0	0	27,048,000	0
Effect of convertible senior notes (in shares)	0	0	36,652,000	0
Weighted-average shares of common stock outstanding and potential dilutive common shares outstanding (in shares)	243,106,000	223,099,000	301,459,000	219,827,000
Net Earnings (Loss) per Share
Basic (in dollars per share)	$ (0.22)	$ (0.29)	$ 0.75	$ (0.55)
Diluted (in dollars per share)	$ (0.22)	$ (0.29)	$ 0.65	$ (0.55)