Inventories (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Sep. 30, 2012	Jun. 30, 2012
Inventory, Net [Abstract]
Total inventories	$ 53,998	$ 67,334	$ 38,413
Gas Utility Natural Gas [Member]
Inventory, Net [Abstract]
Total inventories	43,052	57,663	27,761
Materials, Supplies and Other [Member]
Inventory, Net [Abstract]
Total inventories	$ 10,946	$ 9,671	$ 10,652