Quarterly report pursuant to Section 13 or 15(d)

Related Party Transactions - Schedule of Related Party Receivable and Payables Balances (Parenthetical) (Details)

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Related Party Transactions - Schedule of Related Party Receivable and Payables Balances (Parenthetical) (Details) - Stack's Bowers Galleries
$ in Millions
Dec. 31, 2020
USD ($)
loan
Jun. 30, 2020
USD ($)
Related Party Transaction [Line Items]    
Number of credit lines | loan 2  
Receivables, Net    
Related Party Transaction [Line Items]    
Short term loan receivable $ 0.2  
September 19, 2017 Loan Agreement    
Related Party Transaction [Line Items]    
Short term loan receivable 0.1 $ 0.7
September 19, 2017 Loan Agreement | Secured Loans Receivable    
Related Party Transaction [Line Items]    
Short term loan receivable 0.1  
March 1, 2018 Loan Agreement    
Related Party Transaction [Line Items]    
Short term loan receivable 0.0 $ 8.0
March 1, 2018 Loan Agreement | Secured Loans Receivable    
Related Party Transaction [Line Items]    
Short term loan receivable $ 0.0