Note 10 - Fair Value Measurements - Stock Purchase Warrant Assumptions (Details)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Measurement Input, Risk Free Interest Rate [Member]
Warrant assumption	0.0026	0.0033
Measurement Input, Risk Free Interest Rate [Member] | Minimum [Member]
Warrant assumption			0.0165
Measurement Input, Risk Free Interest Rate [Member] | Maximum [Member]
Warrant assumption			0.0167
Measurement Input, Expected Term [Member]
Warrant assumption	5	5	5
Measurement Input, Price Volatility [Member]
Warrant assumption	1	1	1
Measurement Input, Expected Dividend Rate [Member]
Warrant assumption	0	0	0