| 
           Investments, deposits and other assets (Narrative) (Details) (USD $) 
        In Thousands, unless otherwise specified  | 
        3 Months Ended | 12 Months Ended | 
|---|---|---|
| 
           Mar. 31, 2011 
         | 
        
           Sep. 30, 2011 
         | 
      |
| Investments, deposits and other assets [Abstract] | ||
| Realized gains | $ 139 | |
| Realized losses | (1,685) | |
| Recorded cooperative allocated surplus | $ 1,685 | 
| X | ||||||||||
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- Details 
          
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- Definition 
          The amount of patronage earnings retained within the cooperative during the year. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          This item represents the gain realized during the period from the sale of trading securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          This item represents the loss realized during the period from the sale of trading securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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