Note 8 - Income Taxes - Reconciliation of Effective Tax Rate (Details)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory rate		34.00%	34.00%	34.00%
State tax		(5.59%)	(14.56%)	1.94%
General Business Credits		(2.72%)	(9.25%)
General Business Credits				(15.92%)
Stock-based compensation		(21.55%)	14.36%	(19.19%)
Foreign Rate Differential		(0.50%)	(0.16%)	(1.47%)
Change in Federal Tax Rate		60.98%
Other*	[1]	0.65%	(2.15%)	(1.35%)
Meals and Entertainment*	[1]	2.15%	7.56%	(3.23%)
Valuation allowance		(218.17%)	(24.57%)	(31.63%)
Effective tax rate		(150.75%)	5.23%	(5.01%)

[1] Other balance in 2016 and 2015 was reclassified for consistency with current year.