INCOME TAXES Deferred Tax Assets Liabilities (Details) (USD $) In Thousands	Sep. 30, 2011	Sep. 30, 2010
Current Deferred Tax Asset Liability [Abstract]
Total net current deferred tax assets (liabilities)	$ 1,498	$ (25,556)
Noncurrent Deferred Tax Asset Liability [Abstract]
Total net noncurrent deferred tax (liabilities)	(327,782)	(278,551)
Total net deferred tax (liabilities)	(326,284)	(304,107)
Current [Member]
Current Deferred Tax Asset Liability [Abstract]
Over(under) recoverd gas costs	1,865	0
Pension Liability	15,202	9,260
Deferred service contract revenue	3,191	2,838
Other	2,669	2,382
Total current deferred tax assets	22,927	14,480
Over(under) recoverd gas costs	0	(14,738)
Conservation incentive plan	(3,696)	(6,050)
Fair value of derivatives	(16,571)	(18,107)
Other	(1,162)	(1,141)
Total current deferred tax (liabilities)	(21,429)	(40,036)
Noncurrent Deferred Tax Asset Liability [Abstract]
Other	2,669	2,382
Noncurrent [Member]
Current Deferred Tax Asset Liability [Abstract]
Other	6,557	5,149
Fair value of derivatives	(31)	(1,583)
Noncurrent Deferred Tax Asset Liability [Abstract]
Unamortized investment tax credits	3,353	3,526
Other	6,557	5,149
Total noncurrent deferred tax assets	9,910	8,675
Pension/OPEB	(20,116)	(17,765)
Equity investments	(28,255)	(24,460)
Property related items	(258,501)	(212,825)
Remediation costs	(30,459)	(30,582)
Deferred gain	(330)	(11)
Total noncurrent deferred tax (liabilities)	$ (337,692)	$ (287,226)