Note 6 - Share Repurchase Program (Details Textual)			3 Months Ended
	Aug. 13, 2020	Jul. 07, 2017	Sep. 30, 2020 USD ($) shares	Jun. 30, 2020 shares	Mar. 31, 2020 USD ($) shares	Sep. 30, 2019 shares	Jun. 30, 2019 shares	Aug. 31, 2020 shares	Aug. 31, 2019 USD ($) shares	Aug. 15, 2017 shares	Nov. 04, 2015 USD ($) shares	Dec. 31, 2007 shares
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares) | shares								2,700,000	1,800,000	3,300,000	2,000,000	1,000,000
Stock Repurchase Program, Authorized Amount | $									$ 34,000,000		$ 40,000,000
Stock Repurchased and Retired During Period, Shares (in shares) | shares			0	0	53,064	0	0
Stock Repurchased and Retired During Period, Value | $					$ 597,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $			$ 33,400,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased (in shares) | shares			2,600,000
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3	5
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2	3