| Document And Entity Information | Aug. 14, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 14, 2019 |
| Entity Registrant Name | GROUP 1 AUTOMOTIVE INC |
| Entity Central Index Key | 0001031203 |
| Entity Emerging Growth Company | false |
| Entity File Number | 1-13461 |
| Entity Incorporation, State or Country Code | DE |
| 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 |
| Title of each class | Common Stock, par value $0.01 per share |
| Trading Symbol | GPI |
| Name of each exchange on which registered | NYSE |
