Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 119,683	$ 122,549	$ 65,211	$ 99,029
Accounts receivable	806,391	691,732
Prepaid income taxes	21,270	31,387
Other current assets	93,997	75,158
Total Current Assets	1,041,341	920,826
Property and equipment, net	973,483	912,591
Goodwill	3,318,611	2,782,812
Identifiable intangible assets, net	424,647	326,519
Other assets	210,561	184,418
Total Assets	5,968,643	5,127,166	5,002,937
Current Liabilities:
Overdrafts	21,547	29,463
Current portion of long-term debt and notes payable	22,499	22,187
Accounts payable	138,436	128,194
Accrued payroll	135,561	160,562
Accrued vacation	105,325	92,875
Accrued interest	28,588	19,885
Accrued other	163,141	143,166
Income taxes payable	10,634	9,071
Total Current Liabilities	625,731	605,403
Long-term debt, net of current portion	3,478,021	2,677,715
Non-current deferred tax liability	125,020	124,917
Other non-current liabilities	167,120	145,709
Total Liabilities	4,395,892	3,553,744
Redeemable non-controlling interests	607,474	640,818
Stockholders’ Equity:
Common stock	134	134
Capital in excess of par	468,885	463,499
Retained earnings (accumulated deficit)	383,581	359,735
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	852,600	823,368
Non-controlling interests	112,677	109,236
Total Equity	965,277	932,604
Total Liabilities and Equity	5,968,643	5,127,166
Consolidating and Eliminating Adjustments
Current Assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable	0	0
Intercompany receivables	(1,634,525)	(1,658,682)
Prepaid income taxes	0	0
Other current assets	0	0
Total Current Assets	(1,634,525)	(1,658,682)
Property and equipment, net	0	0
Investment in affiliates	(4,665,256)	(4,650,184)
Goodwill	0	0
Identifiable intangible assets, net	0	0
Other assets	(10,331)	(9,989)
Total Assets	(6,310,112)	(6,318,855)
Current Liabilities:
Overdrafts	0	0
Current portion of long-term debt and notes payable	0	0
Accounts payable	0	0
Intercompany payables	(1,634,525)	(1,658,682)
Accrued payroll	0	0
Accrued vacation	0	0
Accrued interest	0	0
Accrued other	0	0
Income taxes payable	0	0
Total Current Liabilities	(1,634,525)	(1,658,682)
Long-term debt, net of current portion	0	0
Non-current deferred tax liability	(10,331)	(9,989)
Other non-current liabilities	0	0
Total Liabilities	(1,644,856)	(1,668,671)
Redeemable non-controlling interests	587,855	624,548
Stockholders’ Equity:
Common stock	0	0
Capital in excess of par	0	0
Retained earnings (accumulated deficit)	(1,410,528)	(1,447,236)
Subsidiary investment	(3,951,090)	(3,932,822)
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	(5,361,618)	(5,380,058)
Non-controlling interests	108,507	105,326
Total Equity	(5,253,111)	(5,274,732)
Total Liabilities and Equity	(6,310,112)	(6,318,855)
Select (Parent Company Only) | Reportable legal entities
Current Assets:
Cash and cash equivalents	73	73	72	11,071
Accounts receivable	0	0
Intercompany receivables	0	0
Prepaid income taxes	18,382	22,704
Other current assets	18,732	13,021
Total Current Assets	37,187	35,798
Property and equipment, net	37,668	39,836
Investment in affiliates	4,534,700	4,521,865
Goodwill	0	0
Identifiable intangible assets, net	3	0
Other assets	33,702	36,494
Total Assets	4,643,260	4,633,993
Current Liabilities:
Overdrafts	21,547	29,463
Current portion of long-term debt and notes payable	19,372	16,635
Accounts payable	13,235	12,504
Intercompany payables	1,575,611	1,595,692
Accrued payroll	5,248	16,736
Accrued vacation	4,368	4,083
Accrued interest	16,594	17,479
Accrued other	39,010	39,219
Income taxes payable	2,417	0
Total Current Liabilities	1,697,402	1,731,811
Long-term debt, net of current portion	2,055,664	2,042,555
Non-current deferred tax liability	0	0
Other non-current liabilities	37,594	36,259
Total Liabilities	3,790,660	3,810,625
Redeemable non-controlling interests	0	0
Stockholders’ Equity:
Common stock	0	0
Capital in excess of par	952,825	947,370
Retained earnings (accumulated deficit)	(100,225)	(124,002)
Subsidiary investment	0	0
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	852,600	823,368
Non-controlling interests	0	0
Total Equity	852,600	823,368
Total Liabilities and Equity	4,643,260	4,633,993
Subsidiary Guarantors | Reportable legal entities
Current Assets:
Cash and cash equivalents	5,502	4,856	6,836	6,467
Accounts receivable	474,559	445,942
Intercompany receivables	1,575,611	1,595,692
Prepaid income taxes	0	5,703
Other current assets	30,119	29,547
Total Current Assets	2,085,791	2,081,740
Property and equipment, net	622,253	622,445
Investment in affiliates	130,556	128,319
Goodwill	2,108,474	2,108,270
Identifiable intangible assets, net	103,335	103,913
Other assets	104,140	98,492
Total Assets	5,154,549	5,143,179
Current Liabilities:
Overdrafts	0	0
Current portion of long-term debt and notes payable	623	740
Accounts payable	81,563	85,096
Intercompany payables	58,914	62,990
Accrued payroll	81,902	98,834
Accrued vacation	60,577	58,043
Accrued interest	7	7
Accrued other	61,671	57,121
Income taxes payable	0	1,190
Total Current Liabilities	345,257	364,021
Long-term debt, net of current portion	108	127
Non-current deferred tax liability	89,619	88,376
Other non-current liabilities	58,098	56,718
Total Liabilities	493,082	509,242
Redeemable non-controlling interests	0	0
Stockholders’ Equity:
Common stock	0	0
Capital in excess of par	0	0
Retained earnings (accumulated deficit)	1,441,767	1,415,978
Subsidiary investment	3,219,700	3,217,959
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	4,661,467	4,633,937
Non-controlling interests	0	0
Total Equity	4,661,467	4,633,937
Total Liabilities and Equity	5,154,549	5,143,179
Non-Guarantor Subsidiaries | Reportable legal entities
Current Assets:
Cash and cash equivalents	3,749	4,561	3,405	5,056
Accounts receivable	139,693	126,279
Intercompany receivables	58,914	62,990
Prepaid income taxes	0	31
Other current assets	12,389	13,693
Total Current Assets	214,745	207,554
Property and equipment, net	82,697	79,653
Investment in affiliates	0	0
Goodwill	0	0
Identifiable intangible assets, net	5,192	5,200
Other assets	34,907	35,523
Total Assets	337,541	327,930
Current Liabilities:
Overdrafts	0	0
Current portion of long-term debt and notes payable	1,298	2,212
Accounts payable	16,998	17,868
Intercompany payables	0	0
Accrued payroll	2,338	4,872
Accrued vacation	13,363	12,607
Accrued interest	13	6
Accrued other	14,262	12,856
Income taxes payable	0	142
Total Current Liabilities	48,272	50,563
Long-term debt, net of current portion	30,002	24,730
Non-current deferred tax liability	774	780
Other non-current liabilities	8,584	8,141
Total Liabilities	87,632	84,214
Redeemable non-controlling interests	0	0
Stockholders’ Equity:
Common stock	0	0
Capital in excess of par	0	0
Retained earnings (accumulated deficit)	(27,180)	(33,368)
Subsidiary investment	277,089	277,084
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	249,909	243,716
Non-controlling interests	0	0
Total Equity	249,909	243,716
Total Liabilities and Equity	337,541	327,930
Non-Guarantor Concentra | Reportable legal entities
Current Assets:
Cash and cash equivalents	110,359	113,059	54,898	76,435
Accounts receivable	192,139	119,511
Intercompany receivables	0	0
Prepaid income taxes	2,888	2,949
Other current assets	32,757	18,897
Total Current Assets	338,143	254,416
Property and equipment, net	230,865	170,657
Investment in affiliates	0	0
Goodwill	1,210,137	674,542
Identifiable intangible assets, net	316,117	217,406
Other assets	48,143	23,898
Total Assets	2,143,405	1,340,919
Current Liabilities:
Overdrafts	0	0
Current portion of long-term debt and notes payable	1,206	2,600
Accounts payable	26,640	12,726
Intercompany payables	0	0
Accrued payroll	46,073	40,120
Accrued vacation	27,017	18,142
Accrued interest	11,974	2,393
Accrued other	48,198	33,970
Income taxes payable	8,217	7,739
Total Current Liabilities	169,325	117,690
Long-term debt, net of current portion	1,392,247	610,303
Non-current deferred tax liability	44,958	45,750
Other non-current liabilities	62,844	44,591
Total Liabilities	1,669,374	818,334
Redeemable non-controlling interests	19,619	16,270
Stockholders’ Equity:
Common stock	0	0
Capital in excess of par	0	0
Retained earnings (accumulated deficit)	(4,059)	64,626
Subsidiary investment	454,301	437,779
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	450,242	502,405
Non-controlling interests	4,170	3,910
Total Equity	454,412	506,315
Total Liabilities and Equity	2,143,405	1,340,919
Select Medical Corporation
Current Assets:
Cash and cash equivalents	119,683	122,549	$ 65,211	$ 99,029
Accounts receivable	806,391	691,732
Intercompany receivables	0	0
Prepaid income taxes	21,270	31,387
Other current assets	93,997	75,158
Total Current Assets	1,041,341	920,826
Property and equipment, net	973,483	912,591
Investment in affiliates	0	0
Goodwill	3,318,611	2,782,812
Identifiable intangible assets, net	424,647	326,519
Other assets	210,561	184,418
Total Assets	5,968,643	5,127,166
Current Liabilities:
Overdrafts	21,547	29,463
Current portion of long-term debt and notes payable	22,499	22,187
Accounts payable	138,436	128,194
Intercompany payables	0	0
Accrued payroll	135,561	160,562
Accrued vacation	105,325	92,875
Accrued interest	28,588	19,885
Accrued other	163,141	143,166
Income taxes payable	10,634	9,071
Total Current Liabilities	625,731	605,403
Long-term debt, net of current portion	3,478,021	2,677,715
Non-current deferred tax liability	125,020	124,917
Other non-current liabilities	167,120	145,709
Total Liabilities	4,395,892	3,553,744
Redeemable non-controlling interests	607,474	640,818
Stockholders’ Equity:
Common stock	0	0
Capital in excess of par	952,825	947,370
Retained earnings (accumulated deficit)	(100,225)	(124,002)
Subsidiary investment	0	0
Total Select Medical Holdings Corporation and Select Medical Corporation Stockholders’ Equity	852,600	823,368
Non-controlling interests	112,677	109,236
Total Equity	965,277	932,604
Total Liabilities and Equity	$ 5,968,643	$ 5,127,166