Note 7 - Income Taxes - Reconciliation of Effective Tax Rate (Details)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
U.S. federal statutory income tax rate		21.00%	34.00%	34.00%
State tax rate		(4.95%)	(5.59%)	(14.56%)
Meals and entertainment	[1]	(2.66%)	2.15%	7.56%
Stock-based compensation		13.66%	(21.55%)	14.36%
SAB 118 Change in Estimate		(2.43%)
Foreign rate differential		0.11%	(0.50%)	(0.16%)
Other	[1]	(1.21%)	0.65%	(2.15%)
General business credit		4.31%	(2.72%)	(9.25%)
Change in Federal Tax Rate			60.98%
Valuation allowance		(155.49%)	(218.17%)	(24.57%)
Effective tax rate		(127.66%)	(150.75%)	5.23%

[1] Other balance in 2017 and 2016 was reclassified for consistency with current year.