Annual report pursuant to Section 13 and 15(d)

REVENUES (Details)

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REVENUES (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disaggregation of Revenue [Line Items]                      
Revenues $ 60,377 $ 58,909 $ 55,480 $ 51,293 $ 52,016 $ 54,610 $ 57,728 $ 57,322 $ 226,059 $ 221,676 $ 231,321
United States                      
Disaggregation of Revenue [Line Items]                      
Revenues                 149,514 157,267 152,187
Dry-Leasing                      
Disaggregation of Revenue [Line Items]                      
Revenues                 16,024 11,482 16,394
Dry-Leasing | United States                      
Disaggregation of Revenue [Line Items]                      
Revenues                 2,562 3,873 1,604
Dry-Leasing | Foreign                      
Disaggregation of Revenue [Line Items]                      
Revenues                 13,462 7,609 14,790
Operating Income                      
Disaggregation of Revenue [Line Items]                      
Revenues                 210,035 210,194 214,927
Operating Income | United States                      
Disaggregation of Revenue [Line Items]                      
Revenues                 146,952 153,394 150,583
Operating Income | Foreign                      
Disaggregation of Revenue [Line Items]                      
Revenues                 63,083 56,800 64,344
Operating Income | Oil and Gas                      
Disaggregation of Revenue [Line Items]                      
Revenues                 195,822 200,454 198,354
Operating Income | Oil and Gas | United States                      
Disaggregation of Revenue [Line Items]                      
Revenues                 139,312 143,654 134,010
Operating Income | Oil and Gas | Foreign                      
Disaggregation of Revenue [Line Items]                      
Revenues                 56,510 56,800 64,344
Operating Income | Emergency Response Services                      
Disaggregation of Revenue [Line Items]                      
Revenues                 14,213 9,740 11,502
Operating Income | Flightseeing                      
Disaggregation of Revenue [Line Items]                      
Revenues                 $ 0 $ 0 $ 5,071