Note 12 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Tax credits	$ 23,501	$ 18,080
Stock-based compensation	2,392	6,237
Deferred compensation	7,895	7,110
Net operating losses	1,150	615
Other expenses not currently deductible	4,617	2,323
Deferred tax assets, gross	39,555	34,365
Valuation allowance	(18,190)	(15,411)
Deferred tax assets, net of valuation allowance	21,365	18,954
Depreciation and amortization	(1,600)	(1,259)
Undistributed foreign earnings	(77)	(77)
Other expenses currently deductible	(1,132)	(425)
Deferred tax liabilities	(2,809)	(1,761)
Net deferred tax assets	$ 18,556	$ 17,193