Annual report pursuant to Section 13 and 15(d)

VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Aeroleo Narrative (Details)

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VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Aeroleo Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Oct. 01, 2015
Jul. 01, 2011
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]              
Investments in and advances to equity investees     $ 126 $ 0 $ 36    
Deferred revenue         $ 0   $ 31,047
Assets     792,097 955,173      
Liabilities     342,650 482,535      
Aeroleo              
Schedule of Equity Method Investments [Line Items]              
Ownership   50.00%          
Voting ownership percentage   20.00%          
Investments in and advances to equity investees   $ 4,800          
Aeroleo | Equity Method Investee              
Schedule of Equity Method Investments [Line Items]              
Notes receivable to related party   $ 6,000          
Notes receivable interest rate   6.00%          
Revenue from related parties       21,400      
Aeroleo | Co-venturer              
Schedule of Equity Method Investments [Line Items]              
Holding period for put/call arrangement (in years) 2 years            
Variable Interest Entity, Not Primary Beneficiary | Aeroleo              
Schedule of Equity Method Investments [Line Items]              
Percent of economic interest 50.00%            
Percent of voting interest 80.00%            
Aeroleo | Aeroleo | Equity Method Investee              
Schedule of Equity Method Investments [Line Items]              
Deferred revenue           $ 42,100  
Aeroleo              
Schedule of Equity Method Investments [Line Items]              
Assets     11,500 12,900      
Liabilities     $ 7,600 $ 9,200