Note 8 - Preferred Stock and Common Stock Warrants - Fair Value Assumptions (Details)	Sep. 30, 2019	Dec. 31, 2018
Measurement Input, Share Price [Member]
Warrant measurement input	5.76	5.4
Measurement Input, Exercise Price [Member]
Warrant measurement input	0.01	0.01
Measurement Input, Risk Free Interest Rate [Member]
Warrant measurement input	0.016	0.025
Measurement Input, Price Volatility [Member]
Warrant measurement input	0.27	0.331
Measurement Input, Expected Term [Member]
Warrant measurement input	2.1	2.7