Inventories (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Inventory, Net [Abstract]
Total inventories	$ 67,334	$ 104,263
Gas Utility natural gas [Member]
Inventory, Net [Abstract]
Total inventories	57,663	95,590
Materials, supplies and other [Member]
Inventory, Net [Abstract]
Total inventories	$ 9,671	$ 8,673