Annual report pursuant to Section 13 and 15(d)

ACQUISITIONS AND DISPOSITIONS Aeroleo (Details)

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ACQUISITIONS AND DISPOSITIONS Aeroleo (Details) - USD ($)
$ in Millions
12 Months Ended
Oct. 01, 2015
Dec. 31, 2017
Dec. 31, 2016
Variable Interest Entity, Not Primary Beneficiary | Aeroleo      
Business Acquisition [Line Items]      
Percent of economic interest 50.00%    
Percent of voting interest 80.00%    
Co-venturer | Aeroleo      
Business Acquisition [Line Items]      
Holding period for put/call arrangement (in years) 2 years    
Era do Brazil      
Business Acquisition [Line Items]      
Remaining ownership percentage acquired 50.00%    
Era do Brazil | Variable Interest Entity, Primary Beneficiary      
Business Acquisition [Line Items]      
Remaining ownership percentage acquired 50.00%    
Aeroleo      
Business Acquisition [Line Items]      
Operating revenue   $ 35.8 $ 29.3
Net income (loss)   $ 3.6 $ 4.4