| 
           Geographic Information (Details) (USD $) In Thousands, unless otherwise specified 
         | 
        3 Months Ended | 
        6 Months Ended | 
         | 
      
      
        | 
           Dec. 31, 2014 
         | 
        
           Dec. 31, 2013 
         | 
        
           Dec. 31, 2014 
         | 
        
           Dec. 31, 2013 
         | 
        
           Jun. 30, 2014 
         | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
$ 1,538,871us-gaap_Revenues
 | 
        
$ 1,488,691us-gaap_Revenues
 | 
        
$ 2,992,337us-gaap_Revenues
 | 
        
$ 2,984,716us-gaap_Revenues
 | 
         
 | 
      
      
        | Inventories | 
        
143,111us-gaap_InventoryNet
 | 
         
 | 
        
143,111us-gaap_InventoryNet
 | 
         
 | 
        
150,944us-gaap_InventoryNet
 | 
      
      
        | Restricted and Nonrestricted Inventory, Net | 
        
223,771amrk_RestrictedandNonrestrictedInventoryNet
 | 
         
 | 
        
223,771amrk_RestrictedandNonrestrictedInventoryNet
 | 
         
 | 
        
175,554amrk_RestrictedandNonrestrictedInventoryNet
 | 
      
      
        | Assets | 
        
373,938us-gaap_Assets
 | 
         
 | 
        
373,938us-gaap_Assets
 | 
         
 | 
        
305,138us-gaap_Assets
 | 
      
      
        | Long term assets | 
        
11,347us-gaap_NoncurrentAssets
 | 
         
 | 
        
11,347us-gaap_NoncurrentAssets
 | 
         
 | 
        
9,815us-gaap_NoncurrentAssets
 | 
      
      
        | United States | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
1,345,428us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_US
 | 
        
1,256,344us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_US
 | 
        
2,658,914us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_US
 | 
        
2,556,790us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
      
      
        | Inventories | 
        
201,825us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
        
201,825us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
        
159,145us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = country_US
 | 
      
      
        | Assets | 
        
350,982us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
        
350,982us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
        
285,092us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US
 | 
      
      
        | Long term assets | 
        
11,267us-gaap_NoncurrentAssets / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
        
11,267us-gaap_NoncurrentAssets / us-gaap_StatementGeographicalAxis = country_US
 | 
         
 | 
        
9,726us-gaap_NoncurrentAssets / us-gaap_StatementGeographicalAxis = country_US
 | 
      
      
        | Europe | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
64,460us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
        
121,760us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
        
119,410us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
        
192,064us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
      
      
        | Inventories | 
        
9,475us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
        
9,475us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
        
10,500us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
      
      
        | Assets | 
        
10,485us-gaap_Assets / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
        
10,485us-gaap_Assets / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
        
14,137us-gaap_Assets / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
      
      
        | Long term assets | 
        
80us-gaap_NoncurrentAssets / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
        
80us-gaap_NoncurrentAssets / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
         
 | 
        
89us-gaap_NoncurrentAssets / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
 | 
      
      
        | North America, excluding USA | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
110,057us-gaap_Revenues / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
        
100,502us-gaap_Revenues / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
        
181,836us-gaap_Revenues / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
        
177,268us-gaap_Revenues / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
         
 | 
      
      
        | Inventories | 
        
3,846us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
         
 | 
        
3,846us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
         
 | 
        
4,091us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
      
      
        | Assets | 
        
3,846us-gaap_Assets / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
         
 | 
        
3,846us-gaap_Assets / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
         
 | 
        
4,091us-gaap_Assets / us-gaap_StatementGeographicalAxis = amrk_NorthAmericaexcludingUSAMember
 | 
      
      
        | Asia Pacific | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
18,732us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AsiaPacificMember
 | 
        
9,206us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AsiaPacificMember
 | 
        
30,044us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AsiaPacificMember
 | 
        
56,533us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AsiaPacificMember
 | 
         
 | 
      
      
        | Africa | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
25us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AfricaMember
 | 
        
0us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AfricaMember
 | 
        
25us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AfricaMember
 | 
        
0us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_AfricaMember
 | 
         
 | 
      
      
        | Australia | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
167us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_AU
 | 
        
879us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_AU
 | 
        
2,106us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_AU
 | 
        
2,029us-gaap_Revenues / us-gaap_StatementGeographicalAxis = country_AU
 | 
         
 | 
      
      
        | South America | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Revenue | 
        
2us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_SouthAmericaMember
 | 
        
0us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_SouthAmericaMember
 | 
        
2us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_SouthAmericaMember
 | 
        
32us-gaap_Revenues / us-gaap_StatementGeographicalAxis = us-gaap_SouthAmericaMember
 | 
         
 | 
      
      
        | Asia | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Segment Reporting Information [Line Items] | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Inventories | 
        
8,625us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
 | 
         
 | 
        
8,625us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
 | 
         
 | 
        
1,818us-gaap_InventoryNet / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
 | 
      
      
        | Assets | 
        
$ 8,625us-gaap_Assets / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
 | 
         
 | 
        
$ 8,625us-gaap_Assets / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
 | 
         
 | 
        
$ 1,818us-gaap_Assets / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
 |