Commitments and Contingencies (Details) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015 USD ($) $ / MMcf MMcf	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) $ / MMcf MMcf	Jun. 30, 2014 USD ($)
Mid-Tex Division [Member]
Long Term Purchase Commitment [Line Items]
Significant Purchase Commitment Amount | $	$ 21.2	$ 27.8	$ 93.2	$ 81.9
Nonregulated Segment [Member]
Long Term Purchase Commitment [Line Items]
Significant Purchase Commitment Amount | $	$ 203.3	$ 383.2	$ 925.4	$ 1,354.5
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	36,600		36,600
Long Term Purchase Commitment Minimum Quantity Required One To Three Years	35,200		35,200
Inventories Under Indexed Contracts [Member] | Nonregulated Segment [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year	99,100		99,100
Long Term Purchase Commitment Minimum Quantity Required One To Three Years	22,600		22,600
Long Term Purchase Commitment Minimum Quantity Required After Three Years	200		200
Inventories Under Fixed Price Contracts [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year	4,100		4,100
Inventories Under Fixed Price Contracts [Member] | Nonregulated Segment [Member]
Long Term Purchase Commitment [Line Items]
Purchase Commitment Amount Minimum | $ / MMcf	2.62		2.62
Purchase Commitment Amount Maximum | $ / MMcf	3.23		3.23