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Prepaid and Other Current Assets (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]    
Advances to suppliers for crude oil purchases $ 0 $ 38,300
Collateral posted with broker for derivative instruments 215 2,714
Prepaid insurance 7,547 7,504
Derivative assets 4,296 161
Other 5,221 4,701
Total $ 17,279 $ 53,380