Annual report pursuant to Section 13 and 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
12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Derivative [Line Items]    
Gains (losses) on derivative instruments: $ 15,622 $ 9,654
Futures Commodity And Forwards Contracts And Open Purchase And Sale Commitments    
Derivative [Line Items]    
Unrealized gains (losses) on open future commodity and forward contracts and open sale and purchase commitments, net 2,351 (17,738)
Commodity Contract    
Derivative [Line Items]    
Realized gains on future commodity contracts, net $ 13,271 $ 27,392