Note 5 - Stock-based Compensation (Details Textual)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)
Number of Stock-based Compensation Plans in Effect	3		3
Share-based Payment Arrangement, Expense | $	$ 55,000	$ 13,000	$ 80,000	$ 26,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $	$ 644,000		$ 644,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	0		33,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	0		0
The 2011 Non-employee Director Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	12,000