Information On Oil And Natural Gas Producing Activities (Details)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Southwestern Energy Company [Member]
Results Of Operations For Oil And Gas Producing Activities, Purchasers By Significance [Line Items]
Percentage of revenue	17.00%	20.00%	15.00%
Chesapeake Operating Inc [Member]
Results Of Operations For Oil And Gas Producing Activities, Purchasers By Significance [Line Items]
Percentage of revenue	11.00%	10.00%	13.00%
Apache Corporation [Member]
Results Of Operations For Oil And Gas Producing Activities, Purchasers By Significance [Line Items]
Percentage of revenue	9.00%	6.00%	4.00%
Cheyenne Petroleum [Member]
Results Of Operations For Oil And Gas Producing Activities, Purchasers By Significance [Line Items]
Percentage of revenue	6.00%
Devon Energy Corp [Member]
Results Of Operations For Oil And Gas Producing Activities, Purchasers By Significance [Line Items]
Percentage of revenue	5.00%	7.00%	10.00%