Information on Oil and Natural Gas Producing Activities (Details)	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Southwestern Energy Company [Member]
Summary of sales through various operators/purchasers
Percentage of revenue	15.00%	9.00%	8.00%
Chesapeake Operating Inc [Member]
Summary of sales through various operators/purchasers
Percentage of revenue	13.00%	15.00%	14.00%
Devon Energy Corp [Member]
Summary of sales through various operators/purchasers
Percentage of revenue	10.00%	9.00%	6.00%
Newfield Exploration [Member]
Summary of sales through various operators/purchasers
Percentage of revenue	7.00%	14.00%	15.00%
JMA Energy Company [Member]
Summary of sales through various operators/purchasers
Percentage of revenue	5.00%	7.00%	11.00%