Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Transactions - Summary of Hedging Activities Shows Precious Metal Commodity Inventory Position Net of Open Sale and Purchase Commitments (Details)

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Derivative Instruments and Hedging Transactions - Summary of Hedging Activities Shows Precious Metal Commodity Inventory Position Net of Open Sale and Purchase Commitments (Details) - USD ($)
Sep. 30, 2020
Jun. 30, 2020
Jun. 30, 2019
Derivatives, Fair Value [Line Items]      
Inventories $ 413,181,000 $ 321,281,000  
Precious metals held under financing arrangements [1] 158,756,000 178,577,000  
Inventory and precious metals held under financing arrangements 571,937,000 499,858,000  
Commemorative coin inventory, held at lower of cost or net realizable value (9,000) (17,000) $ (17,000)
Premium on metals position (6,770,000) (3,684,000)  
Precious metal value not hedged (6,779,000) (3,701,000)  
Subtotal 565,158,000 496,157,000  
Commitments at market:      
Open inventory purchase commitments 711,710,000 514,553,000  
Open inventory sales commitments (318,921,000) (309,134,000)  
Margin sale commitments (6,864,000) (14,652,000)  
In-transit inventory no longer subject to market risk (8,089,000) (3,605,000)  
Unhedgeable premiums on open commitment positions 2,970,000 2,779,000  
Borrowed precious metals (153,752,000) (168,206,000)  
Product financing arrangements (101,599,000) (74,678,000)  
Advances on industrial metals 394,000 318,000  
Commitments at market 125,849,000 (52,625,000)  
Precious metal subject to price risk 691,007,000 443,532,000  
Precious metal subject to derivative financial instruments:      
Market value of derivative financial instruments 690,691,000 443,790,000  
Net precious metals subject to commodity price risk 316,000 (258,000)  
Precious metals forward contracts at market values      
Precious metal subject to derivative financial instruments:      
Market value of derivative financial instruments 112,243,000 73,948,000  
Precious metals futures contracts at market values      
Precious metal subject to derivative financial instruments:      
Market value of derivative financial instruments $ 578,448,000 $ 369,842,000  
[1] Includes amounts of the consolidated variable interest entity, which is presented separately in the table below.