Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT - Narrative (Details)

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LONG-TERM DEBT - Narrative (Details) - USD ($)
12 Months Ended
Mar. 07, 2018
Dec. 20, 2015
Dec. 01, 2015
Dec. 07, 2012
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Mar. 06, 2018
Dec. 31, 2015
Dec. 23, 2010
Nov. 24, 2010
Debt Instrument [Line Items]                      
Outstanding borrowings         $ 162,405,000 $ 165,203,000          
Gains (losses) on debt extinguishment         $ (13,000) 175,000 $ 0        
Write off of debt issuance cost           $ 400,000          
7.750% Senior Notes (excluding unamortized discount) | Senior Unsecured Notes Due December 15, 2022                      
Debt Instrument [Line Items]                      
Face amount       $ 200,000,000.0              
Stated interest rate       7.75% 7.75% 7.75%          
Proceeds from issuance of long-term debt       $ 191,900,000              
Outstanding borrowings       200,000,000.0              
face amount         $ 700,000            
Repayments of senior notes         700,000            
Interest paid         100,000            
Gains (losses) on debt extinguishment         100,000            
Promissory notes                      
Debt Instrument [Line Items]                      
Outstanding borrowings         $ 18,317,000 $ 19,980,000          
Promissory notes | Promissory Note to Purchase Heavy Helicopter                      
Debt Instrument [Line Items]                      
Face amount                   $ 27,000,000.0  
Outstanding borrowings   $ 19,000,000                  
Debt instrument, interest rate at year-end         3.50%            
Note required monthly payments   100,000                  
Note required final payment   $ 12,800,000                  
Promissory notes | Promissory Note to Purchase Medium Helicopter                      
Debt Instrument [Line Items]                      
Face amount                     $ 11,700,000.0
Outstanding borrowings     $ 5,900,000                
Debt instrument, interest rate at year-end         3.50%            
Note required monthly payments     100,000.0                
Note required final payment     $ 4,000,000                
Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Line of credit facility, maximum borrowing capacity $ 125,000,000       $ 125,000,000     $ 200,000,000 $ 125,000,000    
Interest coverage ratio 175.00%                    
Senior secured leverage ratio 325.00%                    
Basis spread increase 0.50%                    
Maximum commitment increase amount                 50,000,000    
Commitment fee, unused portion         0.50%            
Remaining borrowing capacity         $ 124,300,000            
Letters of credit outstanding         $ 700,000            
Debt issuance costs           $ 1,300,000          
Senior secured revolving credit facility | Promissory notes                      
Debt Instrument [Line Items]                      
Repayments of borrowings outstanding       $ 190,000,000              
Letter of Credit                      
Debt Instrument [Line Items]                      
Line of credit facility, maximum borrowing capacity                 $ 50,000,000.0    
Base Rate | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread         1.75%            
London Interbank Offered Rate (LIBOR) | Promissory notes | Promissory Note to Purchase Heavy Helicopter                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread   1.81%                  
London Interbank Offered Rate (LIBOR) | Promissory notes | Promissory Note to Purchase Medium Helicopter                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread     1.81%                
London Interbank Offered Rate (LIBOR) | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread         2.75%            
Minimum | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Commitment fee, unused portion         0.375%            
Minimum | Base Rate | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread         1.25%            
Minimum | London Interbank Offered Rate (LIBOR) | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread         2.25%            
Maximum | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Commitment fee, unused portion         0.50%            
Maximum | Base Rate | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread         2.50%            
Maximum | London Interbank Offered Rate (LIBOR) | Senior secured revolving credit facility                      
Debt Instrument [Line Items]                      
Debt instrument, basis spread         3.50%