Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments, Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details)

v3.6.0.2
Derivative Financial Instruments, Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Derivatives, Fair Value    
Derivative Instruments and Hedges, Assets $ 18,379 $ 48,888
Derivative Instruments and Hedges, Liabilities 7,119 3,060
Forward Contracts | Commodity Contracts    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 3,602 292
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 5,163 884
Forward Contracts | Fair Value Hedges    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 14,777 33,797
Swaps | Commodity Contracts    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral   14,799
Derivative Liability, Fair Value, Amount Not Offset Against Collateral   0
Swaps | Interest Rate Swaps    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 1,956 2,176
Not Designated as Hedging Instrument    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 3,602 15,091
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 5,163 884
Not Designated as Hedging Instrument | Accounts Receivable | Forward Contracts | Commodity Contracts    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 3,602 292
Not Designated as Hedging Instrument | Accounts Receivable | Swaps | Commodity Contracts    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral   14,799
Not Designated as Hedging Instrument | Accrued Liabilities | Forward Contracts | Commodity Contracts    
Derivatives, Fair Value    
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 5,163 884
Designated as Hedging Instrument    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 14,777 33,797
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 1,956 2,176
Designated as Hedging Instrument | Other Noncurrent Assets | Forward Contracts | Fair Value Hedges    
Derivatives, Fair Value    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 14,777 33,797
Designated as Hedging Instrument | Other Noncurrent Liabilities | Swaps | Interest Rate Swaps    
Derivatives, Fair Value    
Derivative Liability, Fair Value, Amount Not Offset Against Collateral $ 1,956 $ 2,176