Earnings per Share - Net Income Attributable to the Company, Common Shares Outstanding, and Participating Securities Outstanding (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net income	$ 299,731	$ 198,026	$ 499,949
Less: net income attributable to non-controlling interests	56,240	39,032	97,724
Net income attributable to Select Medical Holdings Corporation	243,491	158,994	402,225
Basic EPS
Less: Distributed and undistributed income attributable to participating securities - Basic EPS	8,773	5,609	13,435
Distributed and undistributed income attributable to common shares	234,718	153,385	388,790
Diluted EPS
Less: Distributed and undistributed income attributable to participating securities - Diluted EPS	8,773	5,609	13,435
Distributed and undistributed income attributable to common shares	$ 234,718	$ 153,385	$ 388,790