COMMITMENTS AND CONTINGENCIES - Commitments (Details) $ in Millions	6 Months Ended
	Mar. 31, 2017 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,484.8
Laclede Gas
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	587.4
Alagasco
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 315.7