Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies Commitment and Contingencies (Operational Contengencies) (Details)

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Commitments and Contingencies Commitment and Contingencies (Operational Contengencies) (Details) - ounce
1 Months Ended 12 Months Ended
Aug. 31, 2016
Apr. 30, 2017
Jun. 30, 2018
Long-term Purchase Commitment [Line Items]      
Term of lease (in years)     5 years
Asahi Refining USA, Inc      
Long-term Purchase Commitment [Line Items]      
Term of lease (in years) 1 year    
Operating leases, renewal term 1 year    
Lease fees, subject to adjustment 6 months    
Supply Commitment | Asahi Refining USA, Inc      
Long-term Purchase Commitment [Line Items]      
Supply commitment, term 3 years    
Supply commitment, renewal term 2 years    
Price subject to adjustment, period 6 months    
Silver Products | AM&ST Associates, LLC      
Long-term Purchase Commitment [Line Items]      
Purchase commitment, period 3 years    
Purchase commitment, renewal term 2 years    
Minimum quantity required (in ounces) 300,000 235,000  
Price subject to adjustment, period 6 months    
Guarantor Subsidiaries | Asahi Refining USA, Inc      
Long-term Purchase Commitment [Line Items]      
Agreement to lease (in ounces) 100,000