Note 7 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets, Valuation Allowance, Total	$ 32,350,000	$ 27,865,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	4,500,000	20,600,000
Deferred Tax Assets, Net, Total	$ 424,000	$ 457,000
Open Tax Year	2011 2012 2013 2014 2015 2016 2017 2018
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 58,000
Foreign Tax Authority [Member]
Deferred Tax Assets, Net, Total	400,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	60,100,000
Operating Loss Carryforwards Without Expiration	18,400,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	6,600,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	31,300,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member] | California Franchise Tax Board [Member]
Tax Credit Carryforward, Amount	8,100,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member] | Massachusetts Department of Revenue [Member]
Tax Credit Carryforward, Amount	$ 300,000