Inventories (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Sep. 30, 2011	Jun. 30, 2011
Inventory, Net [Abstract]
Total inventories	$ 38,413	$ 104,263	$ 58,751
Gas Utility Natural Gas [Member]
Inventory, Net [Abstract]
Total inventories	27,761	95,590	50,082
Materials, Supplies and Other [Member]
Inventory, Net [Abstract]
Total inventories	$ 10,652	$ 8,673	$ 8,669