Note 11 - Income Taxes - Deferred Income Tax Assets (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Temporary differences:
Property and equipment	$ (448,000)	$ (379,000)
Intangible assets	(6,000)	(4,000)
Marketable securities	122,000	122,000
Inventory reserve	45,000	60,000
Accrued expenses and inventory	336,000	355,000
Basis difference in investments	(80,000)	(80,000)
Foreign exchange	(14,000)	(8,000)
AMT/Foreign tax credits	25,000
Other	(65,000)	(26,000)
State income taxes	(56,000)	(21,000)
Net deferred income tax liabilities	$ (141,000)
Net deferred income tax assets		$ 19,000