Note 13 - Equity Incentive Plans - Stock Options Outstanding (Details) - $ / shares	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Low price range (in dollars per share)	$ 0	$ 0
High price range (in dollars per share)	$ 0.50	$ 0.50
Outstanding stock options (in shares)	2,695,000	5,275,000
Weighted average remaining contractual life - outstanding (Year)	3 years 302 days	4 years 32 days
Weighted average outstanding strike price - outstanding (in dollars per share)	$ 0.27	$ 0.26
Vested stock options (in shares)	750,000	400,000
Weighted average remaining contractual life - vested (Year)	2 years 273 days	1 year 153 days
Weighted average outstanding strike price - vested (in dollars per share)	$ 0.22	$ 0.19
Range One [Member]
Low price range (in dollars per share)	0	0
High price range (in dollars per share)	$ 0.20	$ 0.20
Outstanding stock options (in shares)	250,000	300,000
Weighted average remaining contractual life - outstanding (Year)	361 days	1 year 339 days
Weighted average outstanding strike price - outstanding (in dollars per share)	$ 0.17	$ 0.18
Vested stock options (in shares)	250,000	250,000
Weighted average remaining contractual life - vested (Year)	361 days	1 year 175 days
Weighted average outstanding strike price - vested (in dollars per share)	$ 0.17	$ 0.17
Range Two [Member]
Low price range (in dollars per share)	0.21	0.21
High price range (in dollars per share)	$ 0.30	$ 0.30
Outstanding stock options (in shares)	1,720,000	4,250,000
Weighted average remaining contractual life - outstanding (Year)	4 years 14 days	4 years 43 days
Weighted average outstanding strike price - outstanding (in dollars per share)	$ 0.26	$ 0.25
Vested stock options (in shares)	500,000	150,000
Weighted average remaining contractual life - vested (Year)	3 years 229 days	1 year 109 days
Weighted average outstanding strike price - vested (in dollars per share)	$ 0.25	$ 0.22
Range Three [Member]
Low price range (in dollars per share)	0.31	0.31
High price range (in dollars per share)	$ 0.50	$ 0.50
Outstanding stock options (in shares)	725,000	725,000
Weighted average remaining contractual life - outstanding (Year)	4 years 116 days	4 years 299 days
Weighted average outstanding strike price - outstanding (in dollars per share)	$ 0.34	$ 0.34
Vested stock options (in shares)	0	0
Weighted average remaining contractual life - vested (Year)	0 years	0 years
Weighted average outstanding strike price - vested (in dollars per share)	$ 0	$ 0

Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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