Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies (Operational Contengencies) (Details)

v3.19.2
Commitments and Contingencies (Operational Contengencies) (Details) - ounce
1 Months Ended
Aug. 31, 2016
Apr. 30, 2017
Long-term Purchase Commitment [Line Items]    
Purchase commitment, period 3 years  
Purchase commitment, renewal term 2 years  
Minimum quantity required (in ounces) 300,000  
Price subject to adjustment, period 6 months  
Supply commitment, term 3 years  
Supply commitment, renewal term 2 years  
Price subject to adjustment, period 6 months  
Agreement to lease (in ounces) 100,000  
Lease fees, subject to adjustment 6 months  
Asahi Refining USA, Inc    
Long-term Purchase Commitment [Line Items]    
Term of lease (in years) 1 year  
Operating leases, renewal term 1 year  
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)   175,000
Supply Commitment | Asahi Refining USA, Inc    
Long-term Purchase Commitment [Line Items]    
Supply commitment, renewal term 2 years