| Cover | Oct. 16, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 16, 2020 |
| Entity File Number | 001-35965 |
| Entity Registrant Name | GTT COMMUNICATIONS, INC. |
| Entity Central Index Key | 0001315255 |
| Entity Tax Identification Number | 20-2096338 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 7900 Tysons One Place |
| Entity Address, Address Line Two | Suite 1450 |
| Entity Address, City or Town | McLean |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 22102 |
| City Area Code | 703 |
| Local Phone Number | 442-5500 |
| 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 $.0001 per share |
| Trading Symbol | GTT |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
