SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) $ in Thousands	Dec. 31, 2017 USD ($) Bcf	Sep. 30, 2017 USD ($) Bcf
Inventory [Line Items]
Gas in Storage, value | $	$ 203,447	$ 202,063
Gas in Storage, Bcf | Bcf	68.4	75.7
Energy Services
Inventory [Line Items]
Gas in Storage, value | $	$ 144,456	$ 122,884
Gas in Storage, Bcf | Bcf	51.9	53.9
Natural Gas Distribution
Inventory [Line Items]
Gas in Storage, value | $	$ 58,991	$ 79,179
Gas in Storage, Bcf | Bcf	16.5	21.8