Information On Oil And Natural Gas Producing Activities (Details)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Southwestern Energy Company [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Percentage of revenue	20.00%	15.00%	9.00%
Chesapeake Operating Inc [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Percentage of revenue	10.00%	13.00%	15.00%
Devon Energy Corp [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Percentage of revenue	7.00%	10.00%	9.00%
Apache Corporation [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Percentage of revenue	6.00%	4.00%	2.00%
Newfield Exploration [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Percentage of revenue	5.00%	7.00%	14.00%