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COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2017
Nov. 30, 2007
Mar. 31, 2018
Dec. 31, 2011
Contingency related to spectrum fees        
Commitments and contingencies        
Spectrum fees paid       $ 2.6
Litigation proceedings and disputes in Guyana        
Commitments and contingencies        
Period for which litigation proceedings and other disputes have not been the subject of discussions or other significant activity     5 years  
Lawsuit filed by CTL        
Commitments and contingencies        
Damages asserted $ 25.0 $ 200.0    
Legal claims regarding tax filings with the Guyana Revenue Authority        
Commitments and contingencies        
Future payments related to disputed tax assessments     $ 44.1  
Accrued contingent liability     $ 5.0  
Legal claims regarding tax filings with the Guyana Revenue Authority | Minimum        
Commitments and contingencies        
Percentage of return on investment ensured by the government of Guyana     15.00%