Note 5 - Stock-based Compensation (Details Textual)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)
Number of Stock-based Compensation Plans in Effect	3		3
Allocated Share-based Compensation Expense, Total | $	$ 18,000	$ 12,000	$ 44,000	$ 39,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | $	$ 91,000		$ 91,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period			20,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Total			4,000