EARNINGS (LOSS) PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net income (loss) attributable to Oscar Health Inc.	$ 177,368	$ (39,772)
Effect of convertible senior notes	5,782	0
Net income (loss) available to Oscar Health, Inc. common shareholders	$ 183,150	$ (39,772)
Denominator:
Weighted average common shares outstanding, basic (in shares)	231,443,000	216,913,000
Common stock equivalents (in shares)	25,701,000	0
Effect of convertible senior notes (in shares)	36,652,000	0
Weighted-average shares of common stock outstanding and potential dilutive common shares outstanding (in shares)	293,796,000	216,913,000
Net Earnings (Loss) per Share
Basic (in dollars per share)	$ 0.77	$ (0.18)
Diluted (in dollars per share)	$ 0.62	$ (0.18)