Note 9 - Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	34.00%
Federal research credits	$ 3,400
Change in valuation allowance attributable to operations	(3,114)	$ (25,093)
Internal Revenue Service (IRS)
Operating Loss Carryforwards	161,541
Internal Revenue Service (IRS) \| No Expire
Operating Loss Carryforwards	28
State and Local Jurisdiction
State research credits	1,100
State and Local Jurisdiction \| Expire On Various Dates
Operating Loss Carryforwards	$ 34,500

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