Condensed Consolidated Statements of Changes in Equity and Income (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital in Excess of Par	Retained Earnings (Accumulated Deficit)	Total Stockholders’ Equity	Non-controlling Interests
Balance (in shares) at Dec. 31, 2017		134,115,000
Balance at Dec. 31, 2017	$ 932,604	$ 134	$ 463,499	$ 359,735	$ 823,368	$ 109,236
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	33,739			33,739	33,739
Net income attributable to non-controlling interests	4,500					4,500
Issuance of restricted stock (in shares)		4,000
Issuance of restricted stock	0	$ 0	0
Forfeitures of unvested restricted stock (in shares)		(88,000)
Forfeitures of unvested restricted stock	0	$ 0	0
Vesting of restricted stock	4,717		4,717		4,717
Repurchase of common shares (in shares)		(7,000)
Repurchase of common shares	(122)	$ 0	(69)	(53)	(122)
Exercise of stock options (in shares)		80,000
Exercise of stock options	738	$ 0	738		738
Issuance and exchange of non-controlling interests	74,341			74,341	74,341
Distributions to and purchases of non-controlling interests	(84,327)			(83,233)	(83,233)	(1,094)
Redemption adjustment on non-controlling interests	(1,051)			(1,051)	(1,051)
Other	138			103	103	35
Balance (in shares) at Mar. 31, 2018		134,104,000
Balance at Mar. 31, 2018	965,277	$ 134	468,885	383,581	852,600	112,677
Balance (in shares) at Dec. 31, 2017		134,115,000
Balance at Dec. 31, 2017	932,604	$ 134	463,499	359,735	823,368	109,236
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	113,167
Balance (in shares) at Sep. 30, 2018		135,140,000
Balance at Sep. 30, 2018	887,568	$ 135	477,822	296,635	774,592	112,976
Balance (in shares) at Mar. 31, 2018		134,104,000
Balance at Mar. 31, 2018	965,277	$ 134	468,885	383,581	852,600	112,677
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	46,511			46,511	46,511
Net income attributable to non-controlling interests	3,139					3,139
Issuance of restricted stock (in shares)		170,000
Issuance of restricted stock	0	$ 0	0
Vesting of restricted stock	4,845		4,845		4,845
Repurchase of common shares (in shares)		(42,000)
Repurchase of common shares	(767)	$ 0	(421)	(346)	(767)
Exercise of stock options (in shares)		95,000
Exercise of stock options	882	$ 0	882		882
Issuance of non-controlling interests	3,474		1,553		1,553	1,921
Distributions to and purchases of non-controlling interests	(3,274)		(932)	(384)	(1,316)	(1,958)
Redemption adjustment on non-controlling interests	(8,500)			(8,500)	(8,500)
Other	340			(337)	(337)	677
Balance (in shares) at Jun. 30, 2018		134,327,000
Balance at Jun. 30, 2018	1,011,927	$ 134	474,812	420,525	895,471	116,456
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	32,917			32,917	32,917
Net income attributable to non-controlling interests	518					518
Issuance of restricted stock (in shares)		1,048,000
Issuance of restricted stock	0	$ 1	(1)
Vesting of restricted stock	5,497		5,497		5,497
Repurchase of common shares (in shares)		(236,000)
Repurchase of common shares	(4,751)	$ 0	(2,499)	(2,252)	(4,751)
Exercise of stock options (in shares)		1,000
Exercise of stock options	13	$ 0	13		13
Distributions to and purchases of non-controlling interests	(4,419)				0	(4,419)
Redemption adjustment on non-controlling interests	(154,514)			(154,514)	(154,514)
Other	380			(41)	(41)	421
Balance (in shares) at Sep. 30, 2018		135,140,000
Balance at Sep. 30, 2018	$ 887,568	$ 135	477,822	296,635	774,592	112,976
Balance (in shares) at Dec. 31, 2018	135,265,864	135,266,000
Balance at Dec. 31, 2018	$ 916,240	$ 135	482,556	320,351	803,042	113,198
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	40,834			40,834	40,834
Net income attributable to non-controlling interests	4,810					4,810
Issuance of restricted stock (in shares)		21,000
Issuance of restricted stock	0	$ 0	0
Forfeitures of unvested restricted stock (in shares)		(24,000)
Forfeitures of unvested restricted stock	0	$ 0	0
Vesting of restricted stock	5,488		5,488		5,488
Issuance of non-controlling interests	6,837					6,837
Distributions to and purchases of non-controlling interests	(2,480)		259		259	(2,739)
Redemption adjustment on non-controlling interests	(47,470)			(47,470)	(47,470)
Other	291			(122)	(122)	413
Balance (in shares) at Mar. 31, 2019		135,263,000
Balance at Mar. 31, 2019	$ 924,550	$ 135	488,303	313,593	802,031	122,519
Balance (in shares) at Dec. 31, 2018	135,265,864	135,266,000
Balance at Dec. 31, 2018	$ 916,240	$ 135	482,556	320,351	803,042	113,198
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	$ 116,382
Balance (in shares) at Sep. 30, 2019	134,171,529	134,172,000
Balance at Sep. 30, 2019	$ 905,743	$ 134	485,415	269,169	754,718	151,025
Balance (in shares) at Mar. 31, 2019		135,263,000
Balance at Mar. 31, 2019	924,550	$ 135	488,303	313,593	802,031	122,519
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	44,816			44,816	44,816
Net income attributable to non-controlling interests	3,663				0	3,663
Issuance of restricted stock (in shares)		187,000
Issuance of restricted stock	0	$ 0	0		0
Vesting of restricted stock	5,591		5,591		5,591
Repurchase of common shares (in shares)		(936,000)
Repurchase of common shares	(13,620)	$ 0	(8,164)	(5,456)	(13,620)
Exercise of stock options (in shares)		50,000
Exercise of stock options	459	$ 0	459		459
Issuance of non-controlling interests	31,127		6,366		6,366	24,761
Distributions to and purchases of non-controlling interests	(1,416)		14		14	(1,430)
Redemption adjustment on non-controlling interests	270			270	270
Other	510			82	82	428
Balance (in shares) at Jun. 30, 2019		134,564,000
Balance at Jun. 30, 2019	995,950	$ 135	492,569	353,305	846,009	149,941
Increase (Decrease) in Stockholders' Equity
Net income attributable to Select Medical Holdings Corporation	30,732			30,732	30,732
Net income attributable to non-controlling interests	7,202				0	7,202
Issuance of restricted stock (in shares)		1,069,000
Issuance of restricted stock	0	$ 1	(1)		0
Forfeitures of unvested restricted stock (in shares)		(12,000)
Forfeitures of unvested restricted stock	0	$ 0	0		0
Vesting of restricted stock	6,050		6,050		6,050
Repurchase of common shares (in shares)		(1,494,000)
Repurchase of common shares	(23,689)	$ (2)	(13,616)	(10,071)	(23,689)
Exercise of stock options (in shares)		45,000
Exercise of stock options	413	$ 0	413		413
Distributions to and purchases of non-controlling interests	(6,538)				0	(6,538)
Redemption adjustment on non-controlling interests	(104,553)			(104,553)	(104,553)
Other	$ 176			(244)	(244)	420
Balance (in shares) at Sep. 30, 2019	134,171,529	134,172,000
Balance at Sep. 30, 2019	$ 905,743	$ 134	$ 485,415	$ 269,169	$ 754,718	$ 151,025