| Cover | Nov. 02, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 2, 2021 |
| Entity File Number | 001-34465 |
| Entity Registrant Name | SELECT MEDICAL HOLDINGS CORPORATION |
| Entity Central Index Key | 0001320414 |
| Entity Tax Identification Number | 20-1764048 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 4714 Gettysburg Road |
| Entity Address, Address Line Two | P.O. Box 2034 |
| Entity Address, City or Town | Mechanicsburg |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 17055 |
| City Area Code | 717 |
| Local Phone Number | 972-1100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Trading Symbol | SEM |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
