| Document and Entity Information Document and Entity Information | Aug. 17, 2020 |
| Cover Page | |
| Document type | 8-K |
| Amendment flag | false |
| Document period end date | Aug. 17, 2020 |
| Entity registrant name | O Reilly Automotive Inc |
| Entity central index key | 0000898173 |
| Entity incorporation, state | MO |
| Entity file number | 000-21318 |
| Entity tax identification number | 27-4358837 |
| Entity address | 233 South Patterson Avenue |
| Entity address, city | Springfield |
| Entity address, state | MO |
| Entity address, postal zip code | 65802 |
| City area code | 417 |
| Local phone number | 862-6708 |
| Written communications | false |
| Soliciting material | false |
| Pre-commencement tender offer | false |
| Pre-commencement issuer tender offer | false |
| Title of 12(b) security | Common Stock |
| Trading symbol | ORLY |
| Security exchange name | NASDAQ |
| Entity emerging growth company | false |
