Condensed Consolidating Financial Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	$ 1,267,401	$ 1,077,014	$ 3,816,575	$ 3,270,996
Costs and expenses:
Cost of services	1,087,062	939,079	3,247,606	2,788,411
General and administrative	29,975	27,065	90,951	83,415
Depreciation and amortization	50,527	38,772	149,022	119,644
Total costs and expenses	1,167,564	1,004,916	3,487,579	2,991,470
Income (loss) from operations	99,837	72,098	328,996	279,526
Other income and expense:
Loss on early retirement of debt			(10,255)	(19,719)
Equity in earnings of unconsolidated subsidiaries	5,432	4,431	14,914	15,618
Non-operating gain (loss)	2,139	0	9,016	(49)
Interest income (expense)	(50,669)	(37,688)	(147,991)	(116,196)
Income (loss) before income taxes	56,739	38,841	194,680	159,180
Income tax expense (benefit)	14,060	14,017	47,460	59,593
Net income	42,679	24,824	147,220	99,587
Less: Net income attributable to non-controlling interests	9,762	6,362	34,053	23,200
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	32,917	18,462	113,167	76,387
Consolidating and Eliminating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	0	0	0	0
Costs and expenses:
Cost of services	0	0	0	0
General and administrative	0	0	0	0
Depreciation and amortization	0	0	0	0
Total costs and expenses	0	0	0	0
Income (loss) from operations	0	0	0	0
Other income and expense:
Intercompany interest and royalty fees	0	0	0	0
Intercompany management fees	0	0	0	0
Loss on early retirement of debt			0	0
Equity in earnings of unconsolidated subsidiaries	0	0	0	0
Non-operating gain (loss)	0		0	0
Interest income (expense)	0	0	0	0
Income (loss) before income taxes	0	0	0	0
Income tax expense (benefit)	0	0	0	0
Equity in earnings of consolidated subsidiaries	(39,146)	(18,955)	(129,204)	(85,479)
Net income	(39,146)	(18,955)	(129,204)	(85,479)
Less: Net income attributable to non-controlling interests	0	0	0	0
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	(39,146)	(18,955)	(129,204)	(85,479)
Select (Parent Company Only) | Reportable legal entities
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	0	56	0	687
Costs and expenses:
Cost of services	815	667	2,340	1,843
General and administrative	29,791	27,028	87,806	83,291
Depreciation and amortization	2,215	2,355	6,777	5,503
Total costs and expenses	32,821	30,050	96,923	90,637
Income (loss) from operations	(32,821)	(29,994)	(96,923)	(89,950)
Other income and expense:
Intercompany interest and royalty fees	6,357	7,865	22,029	24,760
Intercompany management fees	50,601	51,241	166,749	176,443
Loss on early retirement of debt			(2,229)	(19,719)
Equity in earnings of unconsolidated subsidiaries	0	0	0	0
Non-operating gain (loss)	0		1,654	0
Interest income (expense)	(28,933)	(30,240)	(89,416)	(93,725)
Income (loss) before income taxes	(4,796)	(1,128)	1,864	(2,191)
Income tax expense (benefit)	(1,428)	(1,032)	(83)	(3,230)
Equity in earnings of consolidated subsidiaries	36,285	18,558	111,220	75,348
Net income	32,917	18,462	113,167	76,387
Less: Net income attributable to non-controlling interests	0	0	0	0
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	32,917	18,462	113,167	76,387
Subsidiary Guarantors | Reportable legal entities
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	675,059	654,964	2,072,237	2,019,581
Costs and expenses:
Cost of services	585,110	574,250	1,782,843	1,725,060
General and administrative	184	37	250	124
Depreciation and amortization	19,726	18,015	59,708	57,568
Total costs and expenses	605,020	592,302	1,842,801	1,782,752
Income (loss) from operations	70,039	62,662	229,436	236,829
Other income and expense:
Intercompany interest and royalty fees	(2,578)	(4,328)	(10,502)	(14,029)
Intercompany management fees	(39,262)	(41,031)	(132,733)	(147,042)
Loss on early retirement of debt			0	0
Equity in earnings of unconsolidated subsidiaries	5,424	4,416	14,884	15,555
Non-operating gain (loss)	2,139		7,362	(49)
Interest income (expense)	99	271	220	270
Income (loss) before income taxes	35,861	21,990	108,667	91,534
Income tax expense (benefit)	9,923	8,562	36,112	42,135
Equity in earnings of consolidated subsidiaries	2,861	397	17,984	10,131
Net income	28,799	13,825	90,539	59,530
Less: Net income attributable to non-controlling interests	0	24	97	21
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	28,799	13,801	90,442	59,509
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	187,861	166,113	570,918	487,371
Costs and expenses:
Cost of services	164,643	148,072	486,006	423,025
General and administrative	0	0	0	0
Depreciation and amortization	4,098	3,388	12,205	10,007
Total costs and expenses	168,741	151,460	498,211	433,032
Income (loss) from operations	19,120	14,653	72,707	54,339
Other income and expense:
Intercompany interest and royalty fees	(3,445)	(3,537)	(10,685)	(10,731)
Intercompany management fees	(11,339)	(10,210)	(34,016)	(29,401)
Loss on early retirement of debt			0	0
Equity in earnings of unconsolidated subsidiaries	8	15	30	63
Non-operating gain (loss)	0		0	0
Interest income (expense)	(207)	(20)	(544)	(105)
Income (loss) before income taxes	4,137	901	27,492	14,165
Income tax expense (benefit)	112	145	350	428
Equity in earnings of consolidated subsidiaries	0	0	0	0
Net income	4,025	756	27,142	13,737
Less: Net income attributable to non-controlling interests	1,164	359	9,158	3,606
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	2,861	397	17,984	10,131
Non-Guarantor Concentra | Reportable legal entities
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	404,481	255,881	1,173,420	763,357
Costs and expenses:
Cost of services	336,494	216,090	976,417	638,483
General and administrative	0	0	2,895	0
Depreciation and amortization	24,488	15,014	70,332	46,566
Total costs and expenses	360,982	231,104	1,049,644	685,049
Income (loss) from operations	43,499	24,777	123,776	78,308
Other income and expense:
Intercompany interest and royalty fees	(334)	0	(842)	0
Intercompany management fees	0	0	0	0
Loss on early retirement of debt			(8,026)	0
Equity in earnings of unconsolidated subsidiaries	0	0	0	0
Non-operating gain (loss)	0		0	0
Interest income (expense)	(21,628)	(7,699)	(58,251)	(22,636)
Income (loss) before income taxes	21,537	17,078	56,657	55,672
Income tax expense (benefit)	5,453	6,342	11,081	20,260
Equity in earnings of consolidated subsidiaries	0	0	0	0
Net income	16,084	10,736	45,576	35,412
Less: Net income attributable to non-controlling interests	8,598	5,979	24,798	19,573
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	7,486	4,757	20,778	15,839
Select Medical Corporation
Condensed Financial Statements, Captions [Line Items]
Net operating revenues	1,267,401	1,077,014	3,816,575	3,270,996
Costs and expenses:
Cost of services	1,087,062	939,079	3,247,606	2,788,411
General and administrative	29,975	27,065	90,951	83,415
Depreciation and amortization	50,527	38,772	149,022	119,644
Total costs and expenses	1,167,564	1,004,916	3,487,579	2,991,470
Income (loss) from operations	99,837	72,098	328,996	279,526
Other income and expense:
Intercompany interest and royalty fees	0	0	0	0
Intercompany management fees	0	0	0	0
Loss on early retirement of debt			(10,255)	(19,719)
Equity in earnings of unconsolidated subsidiaries	5,432	4,431	14,914	15,618
Non-operating gain (loss)	2,139	0	9,016	(49)
Interest income (expense)	(50,669)	(37,688)	(147,991)	(116,196)
Income (loss) before income taxes	56,739	38,841	194,680	159,180
Income tax expense (benefit)	14,060	14,017	47,460	59,593
Equity in earnings of consolidated subsidiaries	0	0	0	0
Net income	42,679	24,824	147,220	99,587
Less: Net income attributable to non-controlling interests	9,762	6,362	34,053	23,200
Net income attributable to Select Medical Holdings Corporation and Select Medical Corporation	$ 32,917	$ 18,462	$ 113,167	$ 76,387