Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments - Summary of Open Contracts and Closed Contracts (Not yet Settled) Commodity Derivative Contracts (Details)

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Derivative Financial Instruments - Summary of Open Contracts and Closed Contracts (Not yet Settled) Commodity Derivative Contracts (Details)
$ in Thousands
Dec. 31, 2018
USD ($)
Derivatives Fair Value [Line Items]  
Prepaid and other assets – current $ 60,687
Other assets – non-current 21,275
Open Contracts and Closed Contracts - Not Yet Settled  
Derivatives Fair Value [Line Items]  
Prepaid and other assets – current 60,687
Other assets – non-current $ 21,275