SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) $ in Thousands	Sep. 30, 2017 USD ($) Bcf	Sep. 30, 2016 USD ($) Bcf
Public Utilities, Inventory [Line Items]
Gas in Storage | $	$ 202,063	$ 206,251
Bcf | Bcf	75.7	83.3
Energy Services
Public Utilities, Inventory [Line Items]
Gas in Storage | $	$ 122,884	$ 130,493
Bcf | Bcf	53.9	62.0
Natural Gas Distribution
Public Utilities, Inventory [Line Items]
Gas in Storage | $	$ 79,179	$ 75,758
Bcf | Bcf	21.8	21.3