EMPLOYEE BENEFIT PLANS, Defined Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified			3 Months Ended				3 Months Ended		3 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2011 Pension [Member]	Dec. 31, 2010 Pension [Member]	Dec. 31, 2011 Pension [Member] Minimum [Member]	Sep. 30, 2011 Pension [Member] Minimum [Member]	Dec. 31, 2011 Pension [Member] Maximum [Member]	Sep. 30, 2011 Pension [Member] Maximum [Member]	Dec. 31, 2011 Pension Plans Excluding Pension Equalization Plan, Defined Benefit [Member]	Dec. 31, 2011 OPEB [Member]	Dec. 31, 2010 OPEB [Member]	Sep. 30, 2011 OPEB [Member] Minimum [Member]	Sep. 30, 2011 OPEB [Member] Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Contributions by Employer									$ 20,000
Change in Benefit Obligation [Roll Forward]
Service cost			1,344	1,194						896	836
Interest cost			2,206	2,094						1,283	1,211
Change in plan assets [Roll Forward]
Defined Benefit Plan, Contributions by Employer									20,000
Amounts recognized on Consolidated Balance Sheets, Postemployment benefit liability
Non-current	(94,740)	(114,305)
Amounts Recognized in Regulatory Assets and Accumulated Other Comprehensive Income [Roll Forward]
Recognized actuarial loss			(1,254)	(986)						(724)	(653)
Prior service cost amortization			11	12						6	19
Recognized net initial obligation			0	0						89	89
Components of net periodic cost
Service cost			1,344	1,194						896	836
Interest cost			2,206	2,094						1,283	1,211
Expected return on plan assets			(3,171)	(2,872)						(686)	(618)
Recognized actuarial loss			1,254	986						724	653
Prior service cost amortization			11	12						6	19
Recognized net initial obligation			0	0						89	89
Net periodic cost			$ 1,644	$ 1,414						$ 2,312	$ 2,190
Weighted average assumptions used to determine benefit costs
Compensation increase					2.50%		3.25%
Weighted average assumptions used to determine obligations
Compensation increase						2.50%		3.25%				2.50%	3.25%