Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended					6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Energy Services [Member]	Mar. 31, 2012 Energy Services [Member]	Mar. 31, 2013 Energy Services [Member]	Mar. 31, 2012 Energy Services [Member]	Mar. 31, 2013 Inventories [Member] Energy Services [Member] ft3	Sep. 30, 2012 Inventories [Member] Energy Services [Member] ft3	Mar. 31, 2012 Inventories [Member] Energy Services [Member] ft3	Mar. 31, 2013 SCAAs [Member] Energy Services [Member]	Mar. 31, 2012 SCAAs [Member] Energy Services [Member]	Mar. 31, 2013 SCAAs [Member] Energy Services [Member]	Mar. 31, 2012 SCAAs [Member] Energy Services [Member]	Mar. 31, 2013 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Sep. 30, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Mar. 31, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Mar. 31, 2013 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Mar. 31, 2012 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]
Related Party Transaction [Line Items]
Related party costs incurred	$ 3,012	$ 2,781	$ 4,817	$ 4,906								$ 702	$ 408	$ 5,026	$ 5,330				$ 32,526	$ 30,752
Related party security deposits																16,500	15,000	15,000
Volume of gas storage inventory (in bcf of natural gas)									1,000,000,000	7,600,000,000	1,200,000,000
Natural gas storage inventory, related parties, current									3,315	21,217	4,725
Revenue from related parties					25,428	23,574	45,252	40,656
Purchases from related party					$ 18,213	$ 13,267	$ 37,233	$ 23,319