SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) $ in Thousands	Jun. 30, 2018 USD ($) Bcf	Sep. 30, 2017 USD ($) Bcf
Inventory [Line Items]
Gas in Storage, value | $	$ 136,284	$ 202,063
Gas in Storage, Bcf | Bcf	48.5	75.7
Energy Services
Inventory [Line Items]
Gas in Storage, value | $	$ 86,889	$ 122,884
Gas in Storage, Bcf | Bcf	34.7	53.9
Natural Gas Distribution
Inventory [Line Items]
Gas in Storage, value | $	$ 49,395	$ 79,179
Gas in Storage, Bcf | Bcf	13.8	21.8