| Document and Entity Information | Jun. 15, 2021 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001594109 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Jun. 15, 2021 |
| Entity Registrant Name | GRUBHUB INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36389 |
| Entity Tax Identification Number | 46-2908664 |
| Entity Address, Address Line One | 111 W. Washington Street |
| Entity Address, Address Line Two | Suite 2100 |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60602 |
| City Area Code | (877) |
| Local Phone Number | 585-7878 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.0001 par value per share |
| Trading Symbol | GRUB |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
