Note 5 - Income Taxes - Reconciliation of Effective Rate with Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	4.40%	(4.50%)	0.00%
Permanent differences	0.00%	(8.10%)	0.20%
Stock based compensation	(0.40%)	1.30%	0.10%
Federal R&D Credits	1.60%	(4.70%)	(1.70%)
Foreign taxes, net of federal benefit	(2.20%)	44.50%	20.50%
Difference in tax rate for carryback claim	13.40%	0.00%	0.00%
Effective tax rate	37.80%	49.50%	40.10%