Note 9 - Stockholders' Equity - Assumptions Used to Value Warrants at Grant Date (Details)	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2016
Measurement Input, Expected Term [Member] | The 2016 Warrants [Member]
Warrants, measurement input	0.04	5	0.04
Measurement Input, Expected Term [Member] | The 2019 Warrants [Member]
Warrants, measurement input	4.6
Measurement Input, Price Volatility [Member] | The 2016 Warrants [Member]
Warrants, measurement input	1	0.85	1
Measurement Input, Price Volatility [Member] | The 2019 Warrants [Member]
Warrants, measurement input	0.85
Measurement Input, Expected Dividend Rate [Member] | The 2016 Warrants [Member]
Warrants, measurement input	0	0	0
Measurement Input, Expected Dividend Rate [Member] | The 2019 Warrants [Member]
Warrants, measurement input	0
Measurement Input, Exercise Price [Member] | The 2016 Warrants [Member]
Warrants, measurement input	2.55	0.5	2.55
Measurement Input, Exercise Price [Member] | The 2019 Warrants [Member]
Warrants, measurement input	0.5
Measurement Input, Risk Free Interest Rate [Member] | The 2016 Warrants [Member]
Warrants, measurement input	0.0209	0.025	0.0209
Measurement Input, Risk Free Interest Rate [Member] | The 2019 Warrants [Member]
Warrants, measurement input	0.0176
Measurement Input, Weighted Average of Shares Granted, Fair Value [Member] | The 2016 Warrants [Member]
Warrants, measurement input		0.22
Measurement Input, Weighted Average of Shares Granted, Fair Value [Member] | The 2019 Warrants [Member]
Warrants, measurement input	0.21
Measurement Input, Number of Shares Granted [Member] | The 2016 Warrants [Member]
Warrants, measurement input		1,749,171	201,044