Quarterly report pursuant to Section 13 or 15(d)

Financing Agreements (Details)

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Financing Agreements (Details) - USD ($)
 3 Months Ended 9 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Apr. 30, 2018
Jun. 30, 2017
Mar. 31, 2016
Schedule Of Financing Arrangements [Line Items]              
Interest expense, notes payable $ 226,000   $ 505,000        
Percentage of total expense recognized 6.20%   5.20%        
Effective rate of interest 9.19%   9.30%        
Liability on borrowed metals $ 243,295,000   $ 243,295,000     $ 5,625,000  
Product financing obligation 97,370,000   97,370,000     135,343,000  
Line of Credit | Trading credit facility              
Schedule Of Financing Arrangements [Line Items]              
Interest expense, notes payable $ 2,100,000 $ 1,700,000 $ 5,800,000 $ 4,800,000      
Percentage of total expense recognized 57.90% 64.50% 59.90% 64.30%      
Effective rate of interest 3.97% 3.22% 3.85% 3.08%      
Line of Credit | Trading credit facility | A-Mark | Trading credit facility              
Schedule Of Financing Arrangements [Line Items]              
Line of credit, current borrowing capacity $ 275,000,000   $ 275,000,000       $ 225,000,000
Line of credit, accordion option             $ 50,000,000
Payments of financing costs     1,900,000        
Accumulated amortization of loan cost $ 700,000   $ 700,000     $ 100,000  
Variable rate basis     one-month LIBOR        
Credit facility, interest rate at period end 1.88%   1.88%     1.17%  
Borrowings due on demand $ 210,000,000   $ 210,000,000     $ 180,000,000  
Borrowings available $ 10,200,000   10,200,000     $ 45,600,000  
Line of credit facility, tangible net worth financial covenant     $ 47,500,000        
LIBOR | Line of Credit | Revolving Credit Facility              
Schedule Of Financing Arrangements [Line Items]              
Variable rate     2.50%        
LIBOR | Line of Credit | Bridge Loan              
Schedule Of Financing Arrangements [Line Items]              
Variable rate     4.50%        
Subsequent Event | Line of Credit | Trading credit facility | A-Mark | Trading credit facility              
Schedule Of Financing Arrangements [Line Items]              
Line of credit facility, temporary increase         $ 15,000,000