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Supplemental Disclosures to the Financial Statements - Other Current Assets (Details) - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Prepaid expenses $ 4,768 $ 4,577
Materials and supplies 10,972 10,544
Oil inventories 3,144 3,432
Other 846 846
Total other current assets $ 19,730 $ 19,399