Note 9 - Defined Contribution Plan (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.4	$ 0.4	$ 0.3
Maximum [Member]
Defined Contribution Plan Maximum Percentage of Employee Voluntary Contribution	100.00%