Note 5 - Income Taxes - Components of Net Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets
Allowance for doubtful accounts	$ 15	$ 14
Accrued expenses	112	105
Stock-based compensation	114	79
R&D tax credits	675	578
Total Deferred Tax Assets	916	776
Deferred Tax Liabilities
Excess of tax over book depreciation and amortization	(1,832)	(1,980)
Prepaid expenses	(39)	(39)
Total Deferred Tax Liabilities	(1,871)	(2,019)
Net Deferred Tax Liabilities	$ (955)	$ (1,243)