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Supplemental Disclosures to the Condensed Consolidated Balance Sheets and Condensed Consolidated Statements of Cash Flows - Other Current Assets (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Prepaid expenses $ 6,010 $ 4,656
Oil inventories, materials and supplies 10,386 9,473
Other 238 238
Total $ 16,634 $ 14,367