Annual report pursuant to Section 13 and 15(d)

NATURE OF OPERATIONS AND ACCOUNTING POLICIES - Property and Equipment (Details)

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NATURE OF OPERATIONS AND ACCOUNTING POLICIES - Property and Equipment (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Property, Plant and Equipment [Line Items]      
Interest costs capitalized $ 0.1 $ 0.5 $ 0.1
Helicopters (estimated salvage value at 40% of cost)      
Property, Plant and Equipment [Line Items]      
Useful life 15 years    
Salvage value percentage 40.00%    
Machinery, equipment and spares | Minimum      
Property, Plant and Equipment [Line Items]      
Useful life 5 years    
Machinery, equipment and spares | Maximum      
Property, Plant and Equipment [Line Items]      
Useful life 7 years    
Buildings and leasehold improvements | Minimum      
Property, Plant and Equipment [Line Items]      
Useful life 10 years    
Buildings and leasehold improvements | Maximum      
Property, Plant and Equipment [Line Items]      
Useful life 30 years    
Furniture, Fixtures, Vehicles and Other | Minimum      
Property, Plant and Equipment [Line Items]      
Useful life 3 years    
Furniture, Fixtures, Vehicles and Other | Maximum      
Property, Plant and Equipment [Line Items]      
Useful life 5 years    
Construction in Progress      
Property, Plant and Equipment [Line Items]      
Accumulated capitalized interest costs $ 0.7 $ 1.9