Inventories - Schedule of Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016
Public Utilities, Inventory
Total inventories	$ 37,129	$ 42,340	$ 27,009
Gas Utility natural gas
Public Utilities, Inventory
Total inventories	21,826	29,223	13,561
Materials, supplies and other
Public Utilities, Inventory
Total inventories	$ 15,303	$ 13,117	$ 13,448