Note 4 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Stock compensation expense	$ 1,240	$ 1,882
Goodwill	986	1,490
Royalty accruals	560	560
Bad debt allowance	338	466
Net operating loss carryforwards	10,959	9,146
Credit carry-forwards	841	814
Inventory reserve	206	243
Depreciation	499	502
Other	334	340
Total deferred tax assets	15,963	15,443
Deferred tax liabilities:
Intangible assets	(126)	(220)
Total deferred tax liabilities	(126)	(220)
Net deferred tax asset before valuation allowance	15,837	15,223
Valuation allowances for deferred tax assets	(15,971)	(15,394)	$ (13,044)
Net deferred tax liability	$ (134)	$ (171)