Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended							3 Months Ended					3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Energy Services [Member]	Dec. 31, 2011 Energy Services [Member]	Dec. 31, 2012 Inventories [Member] Energy Services [Member] ft3	Sep. 30, 2012 Inventories [Member] Energy Services [Member] ft3	Dec. 31, 2011 Inventories [Member] Energy Services [Member] ft3	Dec. 31, 2012 SCAAs [Member] Energy Services [Member]	Dec. 31, 2011 SCAAs [Member] Energy Services [Member]	Dec. 31, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Sep. 30, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Dec. 31, 2011 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Dec. 31, 2012 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Dec. 31, 2011 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]
Related Party Transaction [Line Items]
Related party costs incurred	$ 1,805	$ 2,125						$ 4,324	$ 4,921				$ 17,825	$ 22,365
Related party security deposits										16,500	15,000	15,000
Volume of gas storage inventory (in bcf of natural gas)					9,100,000,000	7,600,000,000	7,600,000,000
Natural gas storage inventory, related parties, current					27,251	21,217	35,230
Revenue from related parties			19,824	17,081
Purchases from related party			$ 19,020	$ 10,051