Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 100,217	$ 104,457	$ 433,639	$ 242,391
Other comprehensive income (loss), net of tax:
Gain (loss) on interest rate cap cash flow hedge	(536)	0	6,212	0
Reclassification adjustment for (gains) losses included in net income	12	0	18	0
Net change, net of tax benefit (expense)	(524)	0	6,230	0
Comprehensive income	99,693	104,457	439,869	242,391
Less: Comprehensive income attributable to non-controlling interests	23,289	27,511	81,271	60,670
Comprehensive income attributable to Select Medical Holdings Corporation	$ 76,404	$ 76,946	$ 358,598	$ 181,721