Quarterly report pursuant to Section 13 or 15(d)

REVENUES - Operating Revenue (Details)

v3.10.0.1
REVENUES - Operating Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Disaggregation of Revenue [Line Items]        
Revenues $ 57,728 $ 57,878 $ 115,050 $ 112,405
Dry-leasing | United States        
Disaggregation of Revenue [Line Items]        
Revenues 1,271 297 1,844 530
Dry-leasing | Foreign        
Disaggregation of Revenue [Line Items]        
Revenues 1,985 6,392 3,985 9,551
Operating Income        
Disaggregation of Revenue [Line Items]        
Revenues 54,472 51,189 109,221 102,324
Operating Income | United States        
Disaggregation of Revenue [Line Items]        
Revenues 40,312 36,906 79,444 70,873
Operating Income | Foreign        
Disaggregation of Revenue [Line Items]        
Revenues     29,777  
Operating Income | Oil and Gas        
Disaggregation of Revenue [Line Items]        
Revenues 51,931 46,344 104,082 93,798
Operating Income | Oil and Gas | United States        
Disaggregation of Revenue [Line Items]        
Revenues 37,771 32,061 74,305 62,347
Operating Income | Oil and Gas | Foreign        
Disaggregation of Revenue [Line Items]        
Revenues 14,160 14,283 29,777 31,451
Operating Income | Emergency response services        
Disaggregation of Revenue [Line Items]        
Revenues 2,541 2,709 5,139 6,390
Operating Income | Flightseeing        
Disaggregation of Revenue [Line Items]        
Revenues $ 0 $ 2,136 $ 0 $ 2,136