Note 11 - Income Taxes - Deferred Income Tax Assets (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Temporary differences:
Property and equipment	$ (646,000)	$ (448,000)
Intangible assets	(8,000)	(6,000)
Marketable securities		122,000
Inventory reserve	16,000	45,000
Accrued expenses and inventory	443,000	336,000
Basis difference in investments	19,000
Basis difference in investments		(80,000)
Foreign exchange	(13,000)	(14,000)
AMT/Foreign tax credits	50,000	25,000
Other	(30,000)	(65,000)
State income taxes	(55,000)	(56,000)
Net deferred income tax liabilities	$ (224,000)	$ (141,000)