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SUPPLEMENTAL CONSOLIDATED FINANCIAL STATEMENT INFORMATION - Disaggregated Revenues (Details)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
segment
Sep. 30, 2019
USD ($)
Number of business segments | segment     1  
Operating revenues $ 8,738 $ 36,976 $ 77,216 $ 112,216
United States        
Operating revenues $ 8,738 36,814 65,408 96,496
Canada        
Operating revenues   $ 162 $ 11,808 $ 15,720