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Note 9 - Stock Transactions and Stock-based Compensation - Stock Option Valuation Assumptions (Details) - $ / shares
12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Weighted-average value at grant date (in dollars per share)   $ 42.76 $ 58.94
Black-Scholes Option-Pricing Model [Member]      
Weighted-average value at grant date (in dollars per share) $ 130.07 $ 185.6  
Expected life (years) (Year) 3 years 6 months 7 days 3 years 6 months 7 days  
Expected dividend yield 0.07% 0.07%  
Volatility 37.82% 37.29%  
Risk-free interest rate 4.16% 3.55%