TRANSACTIONS WITH RELATED PARTIES (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction [Line Items]
Net trade receivables from affiliates	$ 0	$ 4.7
Due to Related Parties	0.4	0
Interest revenue from affiliates	0	0	0.3
Dividends paid to Laclede Group	5.0
Energen Corporation
Related Party Transaction [Line Items]
Dividends, Cash	$ 32.4	$ 33.3	$ 33.6