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Note 8 - Share-based Compensation - Key Assumptions (Details) - $ / shares
Mar. 01, 2021
Mar. 01, 2020
Dec. 20, 2019
Feb. 01, 2019
Fair value lower range (in dollars per share)   $ 8.76 $ 9.48 $ 16.86
Fair value higher range (in dollars per share)   8.94 9.66 17.16
Exercise price (in dollars per share)   $ 13.98 $ 15.36 $ 28.32
Expected volatility 80.00% 70.00% 70.00% 65.00%
Risk-free rate   1.05% 1.85% 2.61%
Maximum [Member]        
Fair value lower range (in dollars per share) $ 26.04      
Fair value higher range (in dollars per share) 26.58      
Exercise price (in dollars per share) $ 37.98      
Expected term (Year) 1 year 3 months 18 days 1 year 6 months 1 year 7 months 6 days 1 year 3 months 18 days
Risk-free rate 1.18%      
Minimum [Member]        
Expected term (Year) 1 year 1 year 1 year 1 year