Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Transactions (Hedging of Precious Metals Inventory) (Details)

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Derivative Instruments and Hedging Transactions (Hedging of Precious Metals Inventory) (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Jun. 30, 2017
Derivatives, Fair Value [Line Items]    
Inventory $ 311,584 $ 284,659
Commemorative coin inventory, held at lower of cost or market (215) (40)
Premium on metals position (4,129) (4,088)
Inventory value not hedged (4,344) (4,128)
Subtotal 307,240 280,531
Commitments at market:    
Open inventory purchase commitments 567,595 587,687
Open inventory sales commitments (97,564) (121,602)
Margin sale commitments (7,206) (7,936)
In-transit inventory no longer subject to market risk (3,085) (3,931)
Unhedgable premiums on open commitment positions 500 495
Inventory borrowed from suppliers (15,010) (5,625)
Product financing arrangements (124,864) (135,343)
Advances on industrial metals 786 1,580
Inventory subject to price risk 628,392 595,856
Inventory subject to derivative financial instruments:    
Market value of derivative financial instruments 627,680 595,681
Net inventory subject to commodity price risk 712 175
Precious metals forward contracts at market values    
Inventory subject to derivative financial instruments:    
Market value of derivative financial instruments 465,861 462,231
Precious metals futures contracts at market values    
Inventory subject to derivative financial instruments:    
Market value of derivative financial instruments $ 161,819 $ 133,450