COMMON STOCK EQUITY - ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period				$ (5,594)	$ (1,621)
Other comprehensive income (loss), before reclassifications, net of tax				(717)	60
Amounts reclassified from accumulated other comprehensive income, net of tax				1,081	615
Other comprehensive (loss) income		$ (318)	$ 834	364	675
Balance as of end of period		(5,230)	(946)	(5,230)	(946)
Tax on other comprehensive income before reclassifications				(465)	59
Tax on amounts reclassified from accumulated other comprehensive income				708	411
Tax on net current-period other comprehensive income				243	470
Available for Sale Securities [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period				4,782	5,400
Other comprehensive income (loss), before reclassifications, net of tax				(461)	216
Amounts reclassified from accumulated other comprehensive income, net of tax				0	0
Other comprehensive (loss) income				(461)	216
Balance as of end of period		4,321	5,616	4,321	5,616
Tax on other comprehensive income before reclassifications				(319)	150
Tax on amounts reclassified from accumulated other comprehensive income				0	0
Tax on net current-period other comprehensive income				(319)	150
Cash Flow Hedges [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period				(93)	12
Other comprehensive income (loss), before reclassifications, net of tax				(256)	(156)
Amounts reclassified from accumulated other comprehensive income, net of tax	[1]			349	132
Other comprehensive (loss) income				93	(24)
Balance as of end of period		0	(12)	0	(12)
Tax on other comprehensive income before reclassifications				(146)	(91)
Tax on amounts reclassified from accumulated other comprehensive income				202	77
Tax on net current-period other comprehensive income				56	(14)
Postemployment Benefit Obligation [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period				(10,283)	(7,033)
Other comprehensive income (loss), before reclassifications, net of tax				0	0
Amounts reclassified from accumulated other comprehensive income, net of tax	[2]			732	483
Other comprehensive (loss) income				732	483
Balance as of end of period		$ (9,551)	$ (6,550)	(9,551)	(6,550)
Tax on other comprehensive income before reclassifications				0	0
Tax on amounts reclassified from accumulated other comprehensive income				506	334
Tax on net current-period other comprehensive income				$ 506	$ 334

[1] Consists of realized losses related to foreign currency derivatives, which are reclassified to gas purchases in the Unaudited Condensed Consolidated Statements of Operations.

[2] Included in the computation of net periodic pension cost, a component of operations and maintenance expense in the Unaudited Condensed Consolidated Statements of Operations.