Note 13 - Equity-based Compensation - Weighted-average Assumptions Used in Determining the Value of Options Granted to Non-employees (Details) - Nonemployees [Member] - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Expected price volatility	85.03%	87.41%
Expected term (Year)	10 years	10 years
Risk-free interest rate	2.94%	2.27%
Dividend yield	0.00%	0.00%
Weighted-average fair value of options granted during the period (in dollars per share)	$ 1.99	$ 2.40

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the expected term of a nonvested share or option award issued to other than an employee.

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Period an equity-based award is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated measure of the percentage amount by which a share price is expected to fluctuate during the expected term of a nonvested share or option award issued to other than an employee.

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The risk-free interest rate assumption that is used in valuing a nonvested share or option award issued to other than an employee.

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