Note 6 - Stock-based Compensation (Details Textual)	3 Months Ended
	Mar. 31, 2021 USD ($) shares	Mar. 31, 2020 USD ($) shares	Aug. 31, 2020 shares
Number of Stock-based Compensation Plans in Effect	3
Share-based Payment Arrangement, Expense | $	$ 57,000	$ 62,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $	$ 122,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	67,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures, Total (in shares)	0	0
The 2011 Non-employee Director Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)			200,000