Note 4 - Stock-based Compensation  | 
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| Notes to Financial Statements | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share-based Payment Arrangement [Text Block] | 
 For the   three -month periods ended  March  
31,  2021  and 2020,  our total stock-based compensation expense, which includes reversals of expense for certain forfeited or cancelled awards, was approximately $121,000  and $39,000,  respectively. We have not three -month periods ended  March  
31,  2021  and 2020. 
A summary of the status of our stock options as of    March  
31,  2021,  and changes during the three -month period then ended, is presented below.
 The weighted average grant date fair value per stock option granted during the   three -month period ended  March 31, 2021  was $1.87.  Key assumptions used in the Black-Scholes option pricing model for stock options granted during the three -month period ended  March 31, 2021  were the Company's stock price, an expected volatility rate of 90.14%,  a risk-free rate of 0.67%,  and an expected life of 5.97  years. A summary of the status of our unvested restricted stock as of    March  
31,  2021,  and changes during the three -month period then ended, is presented below.
 As of  
 March  
31,  2021,  there was approximately $595,000  of total unrecognized compensation expense related to unvested stock-based awards, which we expect to recognize over the remaining weighted average vesting term of 1.6  years. | 
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