Note 8 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Net operating loss carryforwards	$ 21,175	$ 32,644
Net operating loss carryforwards of foreign subsidiaries	374	374
Book over tax depreciation	(14)	(48)
Stock-based compensation expense	25	38
Other	94	124
Deferred tax assets	21,654	33,132
Valuation allowance for deferred tax assets	(21,654)	(33,132)
Deferred tax assets, net of allowance