Note 9 - Fair Value Measurement - Fair Value Assumptions (Details)	Mar. 31, 2019	Dec. 31, 2018
Measurement Input, Expected Dividend Rate [Member]
Risk free interest rate	0	0
Minimum [Member] | Measurement Input, Risk Free Interest Rate [Member]
Risk free interest rate	0.0255	0.027
Minimum [Member] | Measurement Input, Price Volatility [Member]
Risk free interest rate	0.884	0.922
Minimum [Member] | Measurement Input, Expected Term [Member] | Conversion Feature Liability [Member]
Risk free interest rate	1.01	1.25
Minimum [Member] | Measurement Input, Expected Term [Member] | Warrant Liability [Member]
Risk free interest rate	0	0
Maximum [Member] | Measurement Input, Risk Free Interest Rate [Member]
Risk free interest rate	0.0255	0.027
Maximum [Member] | Measurement Input, Price Volatility [Member]
Risk free interest rate	0.954	0.97
Maximum [Member] | Measurement Input, Expected Term [Member] | Conversion Feature Liability [Member]
Risk free interest rate	2.01	2.25
Maximum [Member] | Measurement Input, Expected Term [Member] | Warrant Liability [Member]
Risk free interest rate	2.01	2.25