Inventories (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Inventory, Net [Abstract]
Total inventories	$ 80,675	$ 89,661	$ 61,861
Gas Utility Natural Gas [Member]
Inventory, Net [Abstract]
Total inventories	69,117	78,950	51,838
Materials, Supplies and Other [Member]
Inventory, Net [Abstract]
Total inventories	$ 11,558	$ 10,711	$ 10,023