Note 9 - Income Taxes - Reconciliation of the Federal Statutory Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Federal statutory rate	21.00%	21.00%	21.00%
State tax, net of federal benefit	2.70%	2.20%	1.90%
Effect of foreign taxes	3.70%	1.10%	2.10%
Federal tax on foreign income	0.20%	0.40%	0.80%
Valuation allowance	(0.10%)	1.40%	0.60%
Foreign deferred tax liability offset	(0.10%)	(0.20%)	(0.40%)
Research & development tax credits	(0.40%)	(0.60%)	(1.20%)
Stock options	(3.10%)	(2.30%)	(8.80%)
Uncertain tax positions	0.20%	0.30%	1.00%
Other permanent differences	(2.40%)	(0.60%)	0.50%
Other	(0.20%)	(0.30%)	(0.20%)
Effective tax rate	21.50%	22.40%	17.30%