Note 7 - Income Taxes - Reconciliation of Effective Tax Rate (Details)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
U.S. federal statutory income tax rate		21.00%	21.00%	34.00%
State tax rate		2.82%	(4.95%)	(5.59%)	[1]
Meals and entertainment	[1]	(2.83%)	(2.66%)	2.15%
Permanent differences		(2.58%)			[1]
Stock-based compensation		3.78%	13.66%	(21.55%)	[1]
SAB 118 Change in Estimate			(2.43%)		[1]
Foreign rate differential		(0.34%)	0.11%	(0.50%)	[1]
Other	[1]	(0.33%)	(1.21%)	0.65%
General business credit		8.14%	4.31%	(2.72%)	[1]
Change in Federal Tax Rate				60.98%	[1]
Valuation allowance		(38.60%)	(155.49%)	(218.17%)	[1]
Change in prior year reserves		2.53%			[1]
Deferred true-up		5.71%			[1]
Effective tax rate		(0.70%)	(127.66%)	(150.75%)	[1]

[1] Other balance in 2017 was reclassified for consistency with 2018 and 2019.