Financial Information for Subsidiary Guarantors and Non-Guarantor Subsidiaries under Select's 6.375% Senior Notes - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements
Net operating revenues	$ 1,114,401	$ 1,097,166	$ 1,120,675	$ 1,111,361	$ 1,046,265	$ 1,053,795	$ 1,097,631	$ 1,088,330	$ 4,443,603	$ 4,286,021	$ 3,742,736
Costs and expenses:
Cost of services									3,734,176	3,664,843	3,211,541
General and administrative									114,047	106,927	92,052
Bad debt expense									79,491	69,093	59,372
Depreciation and amortization									160,011	145,311	104,981
Total costs and expenses									4,087,725	3,986,174	3,467,946
Income from operations	76,352	72,098	115,663	91,765	55,745	56,162	101,054	86,886	355,878	299,847	274,790
Other income and expense:
Loss on early retirement of debt									(19,719)	(11,626)	0
Equity in earnings of unconsolidated subsidiaries									21,054	19,943	16,811
Non-operating gain (loss)									(49)	42,651	29,647
Interest income (expense)									(154,703)	(170,081)	(112,816)
Income before income taxes									202,461	180,734	208,432
Income tax expense (benefit)									(18,184)	55,464	72,436
Net income									220,645	125,270	135,996
Less: Net income attributable to non-controlling interests									43,461	9,859	5,260
Net income attributable to Select Medical Holdings Corporation	$ 100,797	$ 18,462	$ 42,055	$ 15,870	$ 20,172	$ 6,471	$ 33,935	$ 54,833	177,184	115,411	130,736
Eliminations
Condensed Financial Statements
Net operating revenues									0	0	0
Costs and expenses:
Cost of services									0	0	0
General and administrative									0	0	0
Bad debt expense									0	0	0
Depreciation and amortization									0	0	0
Total costs and expenses									0	0	0
Income from operations									0	0	0
Other income and expense:
Intercompany interest and royalty fees									0	0	0
Intercompany management fees									0	0	0
Loss on early retirement of debt									0	0
Equity in earnings of unconsolidated subsidiaries									0	0	0
Non-operating gain (loss)									0	0	0
Interest income (expense)									0	0	0
Income before income taxes									0	0	0
Income tax expense (benefit)									0	0	0
Equity in earnings of consolidated subsidiaries									(193,209)	(105,506)	(140,046)
Net income									(193,209)	(105,506)	(140,046)
Less: Net income attributable to non-controlling interests									0	0	0
Net income attributable to Select Medical Holdings Corporation									(193,209)	(105,506)	(140,046)
Select (Parent Company Only) | Reportable legal entities
Condensed Financial Statements
Net operating revenues									700	541	724
Costs and expenses:
Cost of services									2,585	2,037	2,029
General and administrative									111,069	106,864	88,227
Bad debt expense									0	0	0
Depreciation and amortization									7,540	5,348	4,292
Total costs and expenses									121,194	114,249	94,548
Income from operations									(120,494)	(113,708)	(93,824)
Other income and expense:
Intercompany interest and royalty fees									32,828	31,083	29,393
Intercompany management fees									220,601	168,915	143,939
Loss on early retirement of debt									(19,719)	(773)
Equity in earnings of unconsolidated subsidiaries									0	0	0
Non-operating gain (loss)									0	33,932	0
Interest income (expense)									(124,406)	(132,066)	(89,160)
Income before income taxes									(11,190)	(12,617)	(9,652)
Income tax expense (benefit)									(8,753)	(14,461)	(7,869)
Equity in earnings of consolidated subsidiaries									179,621	113,567	132,519
Net income									177,184	115,411	130,736
Less: Net income attributable to non-controlling interests									0	0	0
Net income attributable to Select Medical Holdings Corporation									177,184	115,411	130,736
Subsidiary Guarantors | Reportable legal entities
Condensed Financial Statements
Net operating revenues									2,711,321	2,752,676	2,691,851
Costs and expenses:
Cost of services									2,283,360	2,346,487	2,280,986
General and administrative									159	63	(890)
Bad debt expense									44,080	41,737	40,708
Depreciation and amortization									76,268	67,932	56,957
Total costs and expenses									2,403,867	2,456,219	2,377,761
Income from operations									307,454	296,457	314,090
Other income and expense:
Intercompany interest and royalty fees									(17,864)	(16,998)	(23,274)
Intercompany management fees									(180,697)	(140,347)	(120,356)
Loss on early retirement of debt									0	0
Equity in earnings of unconsolidated subsidiaries									20,973	19,838	16,719
Non-operating gain (loss)									(49)	8,719	29,647
Interest income (expense)									381	382	408
Income before income taxes									130,198	168,051	217,234
Income tax expense (benefit)									(3,178)	54,047	85,949
Equity in earnings of consolidated subsidiaries									13,588	(8,061)	7,527
Net income									146,964	105,943	138,812
Less: Net income attributable to non-controlling interests									0	28	245
Net income attributable to Select Medical Holdings Corporation									146,964	105,915	138,567
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed Financial Statements
Net operating revenues									697,547	532,180	464,939
Costs and expenses:
Cost of services									591,641	476,084	400,179
General and administrative									0	0	0
Bad debt expense									14,534	9,206	9,073
Depreciation and amortization									14,258	11,314	10,088
Total costs and expenses									620,433	496,604	419,340
Income from operations									77,114	35,576	45,599
Other income and expense:
Intercompany interest and royalty fees									(14,964)	(14,085)	(6,119)
Intercompany management fees									(39,904)	(28,568)	(23,583)
Loss on early retirement of debt									0	0
Equity in earnings of unconsolidated subsidiaries									81	105	92
Non-operating gain (loss)									0	0	0
Interest income (expense)									(170)	(101)	(2)
Income before income taxes									22,157	(7,073)	15,987
Income tax expense (benefit)									1,186	3,166	(512)
Equity in earnings of consolidated subsidiaries									0	0	0
Net income									20,971	(10,239)	16,499
Less: Net income attributable to non-controlling interests									6,736	(2,346)	8,899
Net income attributable to Select Medical Holdings Corporation									14,235	(7,893)	7,600
Non-Guarantor Concentra | Reportable legal entities
Condensed Financial Statements
Net operating revenues									1,034,035	1,000,624	585,222
Costs and expenses:
Cost of services									856,590	840,235	528,347
General and administrative									2,819	0	4,715
Bad debt expense									20,877	18,150	9,591
Depreciation and amortization									61,945	60,717	33,644
Total costs and expenses									942,231	919,102	576,297
Income from operations									91,804	81,522	8,925
Other income and expense:
Intercompany interest and royalty fees									0	0	0
Intercompany management fees									0	0	0
Loss on early retirement of debt									0	(10,853)
Equity in earnings of unconsolidated subsidiaries									0	0	0
Non-operating gain (loss)									0	0	0
Interest income (expense)									(30,508)	(38,296)	(24,062)
Income before income taxes									61,296	32,373	(15,137)
Income tax expense (benefit)									(7,439)	12,712	(5,132)
Equity in earnings of consolidated subsidiaries									0	0	0
Net income									68,735	19,661	(10,005)
Less: Net income attributable to non-controlling interests									36,725	12,177	(3,884)
Net income attributable to Select Medical Holdings Corporation									32,010	7,484	(6,121)
Select
Condensed Financial Statements
Net operating revenues									4,443,603	4,286,021	3,742,736
Costs and expenses:
Cost of services									3,734,176	3,664,843	3,211,541
General and administrative									114,047	106,927	92,052
Bad debt expense									79,491	69,093	59,372
Depreciation and amortization									160,011	145,311	104,981
Total costs and expenses									4,087,725	3,986,174	3,467,946
Income from operations									355,878	299,847	274,790
Other income and expense:
Intercompany interest and royalty fees									0	0	0
Intercompany management fees									0	0	0
Loss on early retirement of debt									(19,719)	(11,626)	0
Equity in earnings of unconsolidated subsidiaries									21,054	19,943	16,811
Non-operating gain (loss)									(49)	42,651	29,647
Interest income (expense)									(154,703)	(170,081)	(112,816)
Income before income taxes									202,461	180,734	208,432
Income tax expense (benefit)									(18,184)	55,464	72,436
Equity in earnings of consolidated subsidiaries									0	0	0
Net income									220,645	125,270	135,996
Less: Net income attributable to non-controlling interests									43,461	9,859	5,260
Net income attributable to Select Medical Holdings Corporation									$ 177,184	$ 115,411	$ 130,736