| Note 4 - Stock Plans and Stock Based Compensation - Black-Scholes Valuation Model Assumptions (Details) - $ / shares | 9 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Sep. 30, 2015 | Sep. 30, 2014 | ||||||||
| Employee Stock Option [Member] | |||||||||
| Weighted-average fair value per share (in dollars per share) | $ 2.88 | ||||||||
| Risk -free interest rate (1) | [1] | 1.91% | |||||||
| Expected volatility of stock (2) | [2] | 61.84% | |||||||
| Dividend yield | |||||||||
| Expected option life (3) (years) | [3] | 6 years | |||||||
| Director Stock Options [Member] | |||||||||
| Weighted-average fair value per share (in dollars per share) | $ 2.84 | $ 2.73 | |||||||
| Risk -free interest rate (1) | [1] | 2.21% | 2.63% | ||||||
| Expected volatility of stock (2) | [2] | 57.98% | 59.59% | ||||||
| Dividend yield | |||||||||
| Expected option life (3) (years) | [3] | 10 years | 10 years | ||||||
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- Definition Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award. No definition available. 
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
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