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Note 5 - Stockholders' Equity - Employee Stock Purchase Plan Valuation Assumptions (Details) - Employee Stock Purchase Plan [Member]
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Risk-free interest rate 0.10% 0.10%
Dividend yield 0.00% 0.00%
Volatility 59.10% 58.90%
Expected life (years) 180 days 180 days