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 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Disaggregation of Revenue [Line Items]        
Total revenues $ 55,480 $ 57,728 $ 106,773 $ 115,050
Dry-leasing | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenues 882 1,271 1,333 1,844
Dry-leasing | International        
Disaggregation of Revenue [Line Items]        
Total revenues 3,405 1,985 6,418 3,985
Operating Income        
Disaggregation of Revenue [Line Items]        
Total revenues 51,193 54,472 99,022 109,221
Operating Income | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenues 36,694 40,312 70,907 79,444
Operating Income | International        
Disaggregation of Revenue [Line Items]        
Total revenues 14,499 14,160 28,115 29,777
Operating Income | Oil and Gas        
Disaggregation of Revenue [Line Items]        
Total revenues 47,769 51,931 93,851 104,082
Operating Income | Oil and Gas | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenues 33,270 37,771 65,736 74,305
Operating Income | Oil and Gas | International        
Disaggregation of Revenue [Line Items]        
Total revenues 14,499 14,160 28,115 29,777
Operating Income | Emergency response services        
Disaggregation of Revenue [Line Items]        
Total revenues $ 3,424 $ 2,541 $ 5,171 $ 5,139