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Cover Page - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Feb. 28, 2020
Jun. 30, 2019
Cover [Abstract]        
Document Type   10-K/A    
Document Annual Report   true    
Document Period End Date   Dec. 31, 2019    
Document Transition Report   false    
Entity File Number   001-35965    
Entity Registrant Name   GTT Communications, Inc.    
Entity Incorporation, State or Country Code   DE    
Entity Tax Identification Number   20-2096338    
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    
Title of 12(b) Security   Common stock, par value $.0001 per share    
Security Exchange Name   NYSE    
Entity Well-known Seasoned Issuer Yes      
Entity Voluntary Filers   No    
Entity Current Reporting Status   Yes    
Entity Interactive Data Current   Yes    
Entity Filer Category   Large Accelerated Filer    
Entity Small Business   false    
Entity Emerging Growth Company   false    
Entity Shell Company   false    
Entity Public Float       $ 804,979,505
Entity Common Stock, Shares Outstanding     56,737,341  
Documents Incorporated by Reference  
Documents Incorporated by Reference 
The following documents (or parts thereof) are incorporated by reference into the following parts of this Form 10-K/A: None
    
Entity Central Index Key   0001315255    
Current Fiscal Year End Date   --12-31    
Amendment Flag   2019    
Document Fiscal Period Focus   FY    
Document Fiscal Year Focus   false    
Trading Symbol   GTT