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Note 6 - Investments in Marketable Securities (Tables)
 6 Months Ended
Mar. 31, 2019
Notes Tables  
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
   
March 31, 2019
    
September 30, 2018
  
   
 
Aggregate
fair value
    
Amortized/Adjusted
cost basis
    
Pretax net unrealized gains
    
 
Aggregate
fair value
    
Amortized/Adjusted
cost basis
    
Pretax net unrealized gains
  
                                                 
Marketable securities
   $
192,153,000
     $
53,889,000
     $
138,264,000
     $
212,296,000
     $
53,889,000
     $
158,407,000