Note 3 - Fair Value Measurements - Assumptions on Accrued Warrant Liability (Details)	Mar. 31, 2020	Dec. 31, 2019
Measurement Input, Share Price [Member]
Warrants and Rights Outstanding, Measurement Input	0.0166	0.006
Measurement Input, Exercise Price [Member] | Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0364	0.0364
Measurement Input, Exercise Price [Member] | Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	0.204	0.204
Measurement Input, Expected Term [Member] | Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0079	0.0104
Measurement Input, Expected Term [Member] | Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0135	0.016
Measurement Input, Price Volatility [Member] | Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	0.684	0.8459
Measurement Input, Price Volatility [Member] | Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	0.9772	0.9824
Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input	0	0
Measurement Input, Discount Rate [Member] | Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0014	0.0158
Measurement Input, Discount Rate [Member] | Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0019	0.0159