| Document and Entity Information | Oct. 06, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | GROUP 1 AUTOMOTIVE INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001031203 |
| Document Type | 8-K |
| Document Period End Date | Oct. 6, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-13461 |
| Entity Tax Identification Number | 76-0506313 |
| Entity Address, Address Line One | 800 Gessner |
| Entity Address, Address Line Two | Suite 500 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77024 |
| City Area Code | (713) |
| Local Phone Number | 647-5700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | GPI |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
