Note 9 - Fair Value Measurement - Fair Value Assumptions (Details)	Dec. 31, 2018	Dec. 31, 2017
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	0.027	0.0156
Minimum [Member] | Measurement Input, Price Volatility [Member]
Risk free interest rate	0.922	0.87
Minimum [Member] | Measurement Input, Expected Term [Member] | Conversion Feature Liability [Member]
Risk free interest rate	1.25	1.25
Minimum [Member] | Measurement Input, Expected Term [Member] | Warrant Liability [Member]
Risk free interest rate	0	0.25
Maximum [Member] | Measurement Input, Risk Free Interest Rate [Member]
Risk free interest rate	0.027	0.0181
Maximum [Member] | Measurement Input, Price Volatility [Member]
Risk free interest rate	0.97	1.184
Maximum [Member] | Measurement Input, Expected Term [Member] | Conversion Feature Liability [Member]
Risk free interest rate	2.25	3.25
Maximum [Member] | Measurement Input, Expected Term [Member] | Warrant Liability [Member]
Risk free interest rate	2.25	3.25