Note 12 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
R&D tax credits	$ 11,833	$ 10,331
Stock-based compensation	10,040	9,157
Deferred compensation	6,829	5,505
Depreciation and amortization		191
Net operating losses	1,133	1,377
Other expenses not currently deductible	1,852	1,924
Deferred tax assets, gross	31,687	28,485
Valuation allowance	(13,041)	(12,568)
Deferred tax assets, net of valuation allowance	18,646	15,917
Depreciation and amortization	(711)
Undistributed foreign earnings	(1,105)
Deferred tax liabilities	(1,816)
Net deferred tax assets	$ 16,830	$ 15,917