Note 17 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	21.00%
Operating Loss Carryforwards, Annual Limitations	$ 3,200,000	$ 62,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	8,600,000	(35,300,000)	$ 25,700,000
Unrecognized Tax Benefits, Ending Balance	1,281,000	851,000	1,582,000	$ 1,404,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total	0	0	0
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	51,600,000	18,000,000	92,300,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	$ 900,000	100,000	3,000,000
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Open Tax Year	2017 2048 2019 2020
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	$ 26,800,000	1,600,000	76,900,000
Open Tax Year	2016 2017 2018 2019 2020
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	$ 3,400,000	$ 2,700,000	$ 2,300,000
Foreign Tax Authority [Member]
Open Tax Year	2015 2016 2017 2018 2019 2020
Foreign Tax Authority [Member] | Australian Taxation Office [Member]
Operating Loss Carryforwards, Total	$ 6,800,000