Note 7 - Embedded Derivatives and Derivative Warrant Liabilities - Schedule of Inputs to Lattice Model Used to Value Embedded Derivatives (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares
Stock price (in dollars per share)	$ 1.97	$ 1.96
Conversion Rate per $1,000 (in shares) | shares	67.95	67.95
Conversion Price (in dollars per share)	$ 14.72	$ 14.72
Maturity date	Mar. 15, 2020	Mar. 15, 2020
Measurement Input, Risk Free Interest Rate [Member]
Risk-free interest rate	0.02	0.0257
Measurement Input, Price Volatility [Member]
Risk-free interest rate	0.55	1.5
Measurement Input, Entity Credit Risk [Member]
Risk-free interest rate	0.27	0.31