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					9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Energy Services [Member]	Jun. 30, 2011 Energy Services [Member]	Jun. 30, 2012 Energy Services [Member]	Jun. 30, 2011 Energy Services [Member]	Jun. 30, 2012 Inventories [Member] Energy Services [Member] ft3	Sep. 30, 2011 Inventories [Member] Energy Services [Member] ft3	Jun. 30, 2011 Inventories [Member] Energy Services [Member] ft3	Jun. 30, 2012 SCAAs [Member] Energy Services [Member]	Jun. 30, 2011 SCAAs [Member] Energy Services [Member]	Jun. 30, 2012 SCAAs [Member] Energy Services [Member]	Jun. 30, 2011 SCAAs [Member] Energy Services [Member]	Jun. 30, 2012 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Sep. 30, 2011 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Jun. 30, 2011 SCAAs [Member] Other current liabilities [Member] Energy Services [Member]	Jun. 30, 2012 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]	Jun. 30, 2011 Exclusive of transactions pursuant SCAAs [Member] Energy Services [Member]
Related Party Transaction [Line Items]
Related party costs incurred	$ 2,107	$ 1,747	$ 7,013	$ 10,595								$ 8,396	$ 16,566	$ 13,726	$ 19,156				$ 30,752	$ 30,093
Related party security deposits																15,000	15,000	15,000
Volume of gas storage inventory (in bcf of natural gas)									4,100,000,000	7,500,000,000	4,000,000,000
Natural gas storage inventory, related parties, current									10,512	35,686	19,035
Revenue from related parties					12,067	13,529	52,744	74,589
Purchases from related party					$ 13,158	$ 9,351	$ 36,477	$ 44,849