Annual report pursuant to Section 13 and 15(d)

RELATED PARTY TRANSACTIONS Narrative (Details)

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RELATED PARTY TRANSACTIONS Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jul. 31, 2011
Related Party Transaction [Line Items]        
Rental expense $ 5,500,000 $ 5,700,000 $ 4,500,000  
SEACOR        
Related Party Transaction [Line Items]        
Revenue from related parties 0 100,000.0 100,000.0  
Rental expense 400,000      
Amended and Restated Transition Services Agreement | SEACOR        
Related Party Transaction [Line Items]        
Expenses from transactions with related party   600,000 3,000,000  
Training Services | Equity Method Investee        
Related Party Transaction [Line Items]        
Notes receivable to related party 3,700,000 4,000,000    
Dart Helicopter Services LLC and Dart Holding Company Ltd. | Products Purchased | Equity Method Investee        
Related Party Transaction [Line Items]        
Expenses from transactions with related party 2,000,000 1,900,000 2,100,000  
Dart Holding Company Ltd. | Equity Method Investee        
Related Party Transaction [Line Items]        
Notes receivable to related party 2,800,000 3,200,000   $ 5,100,000
Era Training Center | Helicopter, Management and Other Services | Equity Method Investee        
Related Party Transaction [Line Items]        
Expenses from transactions with related party 200,000 200,000 400,000  
Era Training Center | Training Services | Equity Method Investee        
Related Party Transaction [Line Items]        
Expenses from transactions with related party $ 500,000 $ 600,000 $ 500,000