Note 9 - Options and Warrants to Purchase Common Stock - Summary of the Status and Changes of the Options Granted Under the Stock Option Plans and Other Agreements (Details) - $ / shares	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Outstanding at December 31, 2017 (in shares)	57,057,768	21,277,479	17,806,472
Outstanding at December 31, 2017 (in dollars per share)	$ 0.36	$ 0.87	$ 1
Stock options granted (in shares)	4,224,999	35,810,289	3,771,488
Granted (in dollars per share)	$ 0.11	$ 0.06	$ 0.24
Exercised (in shares)
Exercised (in dollars per share)
Forfeited (in shares)	(232,645)	(30,000)	(300,481)
Forfeited (in dollars per share)	$ 1.36		$ 0.83
Outstanding at June 30, 2018 (in shares)	61,050,122	57,057,768	21,277,479
Outstanding at June 30, 2018 (in dollars per share)	$ 0.34	$ 0.36	$ 0.87

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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