Note 10 - Income Taxes - Summary of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net operating loss carryforwards	$ 37,237	$ 34,488	$ 29,217
Federal and state tax credits	21,223	16,404	12,126
Accrued expenses	544	27	478
Patents	360	443	531
Stock-based compensation	1,353	596	92
Other	321	276	8
	61,038	52,234	42,452
Valuation allowance	(61,038)	(52,234)	(42,452)
Net deferred tax asset	$ 0	$ 0	$ 0