Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Energy Services [Member]	Jun. 30, 2012 Energy Services [Member]	Jun. 30, 2013 Energy Services [Member]	Jun. 30, 2012 Energy Services [Member]	Jun. 30, 2013 Inventories [Member] Energy Services [Member] ft3	Sep. 30, 2012 Inventories [Member] Energy Services [Member] ft3	Jun. 30, 2012 Inventories [Member] Energy Services [Member] ft3	Jun. 30, 2013 SCAAs [Member] Energy Services [Member]	Jun. 30, 2012 SCAAs [Member] Energy Services [Member]	Jun. 30, 2013 SCAAs [Member] Energy Services [Member]	Jun. 30, 2012 SCAAs [Member] Energy Services [Member]	Jun. 30, 2013 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Sep. 30, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Jun. 30, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Jun. 30, 2013 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Jun. 30, 2012 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Jun. 30, 2013 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Jun. 30, 2012 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Jun. 30, 2013 SCAAs [Member] Storage_Agreement	Jun. 30, 2013 SCAAs [Member] Energy Services [Member] Storage_Agreement	Jun. 30, 2013 Expires in October 2013 [Member] SCAAs [Member] Storage_Agreement	Jun. 30, 2013 Expires in October 2013 [Member] SCAAs [Member] Energy Services [Member] Storage_Agreement	Jun. 30, 2013 Expires in October 2015 [Member] SCAAs [Member] Storage_Agreement	Jun. 30, 2013 Expires in October 2015 [Member] SCAAs [Member] Energy Services [Member] Storage_Agreement
Related Party Transaction [Line Items]
Number of storage agreements (in storage agreements)																							3	3	1	1	2	2
Related party costs incurred	$ 1,940	$ 2,107	$ 6,757	$ 7,013								$ 21,570	$ 8,396	$ 26,596	$ 13,726				$ 0	$ 0	$ 32,526	$ 30,752
Related party security deposits																16,500	15,000	15,000
Volume of gas storage inventory (in bcf of natural gas)									5,600,000,000	7,600,000,000	4,100,000,000
Natural gas storage inventory, related parties, current									24,389	21,217	10,512
Revenue from related parties					14,956	12,067	60,208	52,744
Purchases from related party					$ 24,426	$ 13,158	$ 61,659	$ 36,477