Note 12 - Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share options	$ 1,884	$ 1,251
Accrued liabilities	526	177
State credits	85
Other		160
Total deferred tax assets	52,550	43,076
Valuation allowance	(46,473)	(43,076)	$ (35,361)	$ (26,413)
Total deferred tax assets	6,077
Other assets	(29)
Intangible assets	(3,418)
Total deferred tax liabilities	(3,447)
State and Local Jurisdiction [Member]
State net operating loss (net of federal)	5,198	4,021
Internal Revenue Service (IRS) [Member]
U.S. federal net operating losses	42,165	32,095
U.S. federal research and development credit	273	155
Her Majesty's Revenue and Customs (HMRC) [Member]
U.K. net operating loss	2,419	$ 5,217
Total deferred tax assets	$ 2,600