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Note 6 - Investments in Marketable Securities (Tables)
 3 Months Ended
Dec. 31, 2018
Notes Tables  
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
   
December 31, 2018
    
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
   $
183,656,000
     $
53,889,000
     $
129,767,000
     $
212,296,000
     $
53,889,000
     $
158,407,000