Note 8 - Related-party Transactions (Details Textual) - Immediate Family Member of Management or Principal Owner [Member] - Grading and Authentication Fees [Member] - USD ($)	3 Months Ended	9 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2018
Related Party Transaction, Other Revenues from Transactions with Related Party	$ 409,000	$ 394,000	$ 793,000	$ 1,649,000
Accounts Receivable, Related Parties, Current	$ 170,000		$ 170,000		$ 127,000

Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant