Quarterly report pursuant to Section 13 or 15(d)

REVENUES - Operating Revenue (Details)

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REVENUES - Operating Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Disaggregation of Revenue [Line Items]    
Total revenues $ 57,056 $ 51,293
Dry-leasing | U.S.    
Disaggregation of Revenue [Line Items]    
Total revenues 190 451
Dry-leasing | International    
Disaggregation of Revenue [Line Items]    
Total revenues 2,886 3,012
Operating Income    
Disaggregation of Revenue [Line Items]    
Total revenues 53,980 47,830
Operating Income | U.S.    
Disaggregation of Revenue [Line Items]    
Total revenues 38,992 34,214
Operating Income | International    
Disaggregation of Revenue [Line Items]    
Total revenues 14,988 13,616
Operating Income | Oil and Gas    
Disaggregation of Revenue [Line Items]    
Total revenues 50,335 46,082
Operating Income | Oil and Gas | U.S.    
Disaggregation of Revenue [Line Items]    
Total revenues 37,054 32,466
Operating Income | Oil and Gas | International    
Disaggregation of Revenue [Line Items]    
Total revenues 13,281 13,616
Operating Income | Emergency response services    
Disaggregation of Revenue [Line Items]    
Total revenues $ 3,645 $ 1,748