BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Sep. 30, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		$ 3,419,594	$ 3,284,357
Subtotal [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		3,382,307	3,252,206
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		2,372,033	2,305,293
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		243,989	260,021
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		566,582	504,885
Midstream [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		199,703	182,007
Home Services and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		106,541	88,880
Intercompany Assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	[1]	$ (69,254)	$ (56,729)

[1] Consists of transactions between subsidiaries that are eliminated and reclassified in consolidation.