Note 11 - Income Taxes - Deferred Income Tax Assets (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Foreign tax credits		$ 3,000
Temporary differences:
Inventory reserve		101,000
Accrued expenses and inventory		334,000
Current deferred income tax assets, net		438,000
Non-current deferred income taxes:
Property and equipment	(379,000)	(683,000)
Intangible assets	(4,000)	(4,000)
Marketable securities	122,000	112,000
Inventory reserve	60,000
Accrued expenses and inventory	355,000
Basis diffence in investments	(80,000)	(129,000)
Foreign exchange	(8,000)	(12,000)
Other	(26,000)	(20,000)
State income taxes	(21,000)	(71,000)
Non-current deferred income tax assets (liabilities)	19,000
Non-current deferred income tax assets (liabilities)		(807,000)
Net deferred income tax assets (liabilities)	$ 19,000
Net deferred income tax assets (liabilities)		$ (369,000)