Note 12 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
R&D tax credits	$ 10,331	$ 9,817
Stock-based compensation	9,157	7,283
Deferred compensation	5,505	6,752
Depreciation and amortization	191	161
Net operating losses	1,377
Other expenses not currently deductible	1,924	3,974
Total deferred tax assets	28,485	27,987
Valuation allowance	(12,568)	(27,354)
Net deferred tax assets	$ 15,917	$ 633