Note 8 - Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	34.00%
Federal research credits	$ 3,200
Change in valuation allowance attributable to operations	(25,093)	$ (936)
Internal Revenue Service (IRS)
Operating Loss Carryforwards	169,100
Internal Revenue Service (IRS) | No Expire
Operating Loss Carryforwards	27
State and Local Jurisdiction
State research credits	1,800
State and Local Jurisdiction | Expire On Various Dates
Operating Loss Carryforwards	$ 70,400