Note 7 - Share-based Compensation (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	$ 0	$ 0	$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 1.72
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			1,698,452
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	5,600,000		$ 5,600,000
Allocated Share-based Compensation Expense, Total	730,000	701,000	$ 2,083,000	1,999,000
Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			0
Non-employees [Member]
Allocated Share-based Compensation Expense, Total	74,000	$ 188,000	$ 150,000	$ 698,000
Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			2 years 255 days
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			1 year 109 days
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 292,000		$ 292,000

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Gross number of share options (or share units) granted during the period.

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