Note 9 - Income Taxes - Schedule of Reconciliation of Theoretical Tax Expense and Actual Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss before taxes, as reported in the consolidated statements of operations	$ (11,235)	$ (16,579)	$ (20,597)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%	34.00%	34.00%
Theoretical tax benefits on the above amount at the US statutory tax rate	$ (3,820)	$ (5,637)	$ (7,003)
Income tax at rate other than the U.S. statutory tax rate	(934)	68	333
Tax advances and non-deductible expenses including equity based compensation expenses	3,123	4,298	1,061
Operating losses and other temporary differences for which valuation allowance was provided	(10,203)	3,001	6,558
Research and Development Tax Credit	1,126	(1,182)
State tax	(563)	(536)	(477)
Impact of rate change	12,121	(360)	(82)
Change in tax reserve for uncertain tax positions	(1,576)	(1,209)	(320)
Other individually immaterial income tax items	33	270	(24)
Income tax expense	$ 2,459	$ 1,131	$ 686