Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2023		Jun. 30, 2023
Accounts and other receivables, allowance for credit loss	$ 0		$ 0
Investments in available-for-sale debt securities, amortized cost	7,414	[1]	7,729
Investments in available-for-sale debt securities, allowance for credit loss	$ 0		$ 0
Common Class A [Member]
Common Stock, Par value (in dollars per share)	$ 0.025		$ 0.025
Common Stock, Shares Authorized (in shares)	28,000,000		28,000,000
Common Stock, Shares, Issued (in shares)	13,866,999		13,866,999
Common Stock, Shares, Outstanding (in shares)	12,303,955		12,496,674
Treasury shares (in shares)	1,563,044		1,370,325
Common Class B [Member]
Common Stock, Par value (in dollars per share)	$ 0.025		$ 0.025
Common Stock, Shares Authorized (in shares)	4,500,000		4,500,000
Common Stock, Shares, Issued (in shares)	0		0
Common Class C [Member]
Common Stock, Par value (in dollars per share)	$ 0.025		$ 0.025
Common Stock, Shares Authorized (in shares)	3,500,000		3,500,000
Common Stock, Shares, Issued (in shares)	2,068,549		2,068,549
Common Stock, Shares, Outstanding (in shares)	2,068,549		2,068,549

[1] Principal payments of $750,000 are due quarterly with a final maturity date in January 2026.