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Information On Oil and Natural Gas Producing Activities (Tables)
 12 Months Ended
Sep. 30, 2012
Information on Oil and Natural Gas Producing Activities [Abstract]  
Summary of sales through various operators or purchasers
                         
    2012     2011     2010  

Southwestern Energy Company

     15 %      9 %      8 % 

Chesapeake Operating, Inc.

     13 %      15 %      14 % 

Devon Energy Corp.

     10 %      9 %      6 % 

Newfield Exploration

     7 %      14 %      15 % 

JMA Energy Company

     5 %      7 %      11 %