SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) $ in Thousands	Sep. 30, 2018 USD ($) Bcf	Sep. 30, 2017 USD ($) Bcf
Public Utilities, Inventory [Line Items]
Gas in Storage | $	$ 184,633	$ 202,063
Bcf | Bcf	59.0	75.7
Energy Services
Public Utilities, Inventory [Line Items]
Gas in Storage | $	$ 90,166	$ 122,884
Bcf | Bcf	34.1	53.9
Natural Gas Distribution
Public Utilities, Inventory [Line Items]
Gas in Storage | $	$ 94,467	$ 79,179
Bcf | Bcf	24.9	21.8