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Note 6 - Shareholders' Equity (Details Textual) - USD ($)
1 Months Ended 12 Months Ended
Apr. 30, 1998
Mar. 31, 2019
Mar. 31, 2018
Jan. 25, 2019
Jul. 23, 2018
Jan. 22, 2018
May 08, 2017
Aug. 01, 2011
Nov. 01, 2010
Oct. 31, 2008
Nov. 08, 2006
Preferred Stock, Shares Issued, Total 250,000 3,000 3,000                
Preferred Stock, Par or Stated Value Per Share $ 0.001 $ 0.001 $ 0.001                
Shares Issued, Price Per Share $ 4                    
Payments of Stock Issuance Costs $ 112,187                    
Convertible Preferred Stock, Shares Issued upon Conversion 4.05                    
Preferred Stock, Liquidation Preference Per Share $ 4 $ 4 $ 4                
Preferred Stock, Shares Outstanding, Ending Balance   3,000 3,000                
Stock Repurchase Program, Authorized Amount       $ 30,000,000       $ 20,000,000 $ 20,000,000 $ 20,000,000 $ 20,000,000
Treasury Stock, Shares, Acquired   0 0                
Stock Repurchase Program, Remaining Authorized Repurchase Amount   $ 40,200,000                  
Dividends Payable, Amount Per Share         $ 0.27 $ 0.25 $ 0.20        
Convertible Preferred Stock [Member]                      
Preferred Stock, Shares Outstanding, Ending Balance   2,500 2,500