Note 5 - Inventories (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory Write-down		$ 597,000
Cost of Goods Sold [Member]
Inventory Write-down	$ 33,000	$ 52,000	$ 261,000