Note 10 - 401(k) Retirement Benefit Plan (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%	50.00%
Defined Contribution Plan, Maximum Employee Contribution Percentage, Subject to Employer Matching Contribution	6.00%	6.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	3.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 338	$ 319