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Note 6 - Investments in Marketable Securities (Tables)
 6 Months Ended
Mar. 31, 2020
Notes Tables  
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
   
March 31, 2020
    
September 30, 2019
  
   
Aggregate
fair value
    
Adjusted
cost basis
    
Pretax net unrealized gains
    
Aggregate
fair value
    
Amortized/Adjusted
cost basis
    
Pretax unrealized gains
  
Marketable securities
                                                
Common stocks
   $
136,901,000
     $
53,889,000
     $
83,012,000
     $
194,581,000
     $
53,889,000
     $
140,692,000