Commitments and Contingencies (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2015 USD ($) $ / Mcf MMcf	Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)
Estimated Contractual Demand Fees [Abstract]
2016	$ 7,843
2017	3,522
2018	1,966
2019	426
2020	398
Thereafter	1,101
Total Estimated Contractual Demand Fees	15,256
Mid-Tex Division [Member]
Long Term Purchase Commitment [Line Items]
Significant Purchase Commitment, Amount	113,300	$ 140,900	$ 89,000
Nonregulated Segment [Member]
Long Term Purchase Commitment [Line Items]
Significant Purchase Commitment, Amount	$ 1,141,300	$ 1,687,500	$ 1,246,100
Inventories Under Indexed Contracts [Member] | Mid-Tex Division [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year | MMcf	36,600
Long Term Purchase Commitment Minimum Quantity Required One To Three Years | MMcf	26,800
Inventories Under Indexed Contracts [Member] | Nonregulated Segment [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year | MMcf	101,900
Long Term Purchase Commitment Minimum Quantity Required One To Three Years | MMcf	16,000
Long Term Purchase Commitment Minimum Quantity Required After Three Years | MMcf	500
Inventories Under Fixed Price Contracts [Member] | Nonregulated Segment [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year | MMcf	3,000
Purchase Commitment Amount Minimum | $ / Mcf	2.32
Purchase Commitment Amount Maximum | $ / Mcf	3.23