Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Transactions (Realized Gain (Loss)) (Details)

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Derivative Instruments and Hedging Transactions (Realized Gain (Loss)) (Details) - USD ($)
$ in Thousands
3 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Derivative [Line Items]    
Gains (losses) on derivative instruments: $ (14,644) $ (3,891)
Futures Commodity And Forwards Contracts And Open Purchase And Sale Commitments    
Derivative [Line Items]    
Unrealized losses on open future commodity and forward contracts and open sale and purchase commitments, net (12,257) (18,150)
Commodity Contract    
Derivative [Line Items]    
Realized (losses) gains on future commodity contracts, net $ (2,387) $ 14,259