Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended							3 Months Ended					3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Energy Services [Member]	Dec. 31, 2012 Energy Services [Member]	Dec. 31, 2013 Inventories [Member] Energy Services [Member] ft3	Sep. 30, 2013 Inventories [Member] Energy Services [Member] ft3	Dec. 31, 2012 Inventories [Member] Energy Services [Member] ft3	Dec. 31, 2013 SCAAs [Member] Energy Services [Member]	Dec. 31, 2012 SCAAs [Member] Energy Services [Member]	Dec. 31, 2013 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Sep. 30, 2013 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Dec. 31, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Dec. 31, 2013 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Dec. 31, 2012 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Dec. 31, 2013 SCAAs [Member] Storage_Agreement
Related Party Transaction [Line Items]
Number of storage agreements (in storage agreements)															4
Related party costs incurred	$ 1,843	$ 1,805						$ 6,448	$ 4,324				$ 19,378	$ 17,825
Related party security deposits										10,600	16,500	16,500
Volume of gas storage inventory (in bcf of natural gas)					6,800,000,000	10,400,000,000	9,100,000,000
Natural gas storage inventory, related parties, current					27,052	41,988	27,251
Revenue from related parties			17,116	19,824
Purchases from related party			$ 22,078	$ 19,020