CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Operating revenues
Operating revenues	$ 552,566	$ 576,414	$ 1,225,509	$ 1,083,994	$ 779,667	$ 833,168	$ 1,556,374	$ 1,117,226	$ 3,438,483	$ 4,286,435	$ 4,661,060
Purchased gas cost
Purchased gas cost									2,114,744	2,985,615	3,346,924
Gross profit	249,389	293,171	425,787	355,392	237,160	261,612	444,466	357,582	1,323,739	1,300,820	1,314,136
Operating expenses
Operation and maintenance									453,613	442,965	454,621
Depreciation and amortization									237,525	223,832	208,539
Taxes, other than income									181,073	177,767	187,143
Asset impairments									5,288	30,270	0
Total operating expenses									877,499	874,834	850,303
Operating income	22,791	81,546	202,432	139,471	39,195	31,394	204,624	150,773	446,240	425,986	463,833
Miscellaneous income (expense)									(14,644)	21,184	(591)
Interest charges									141,174	150,763	154,188
Income (loss) before income taxes									290,422	296,407	309,054
Income tax expense (benefit)									98,226	106,819	119,203
Income (loss) from continuing operations	(286)	28,014	102,084	62,384	237	(3,150)	124,293	68,208	192,196	189,588	189,851
Income (loss) from discontinued operations	1,904	3,118	7,027	6,123	1,724	2,584	7,916	5,789	18,172	18,013	15,988
Gain on sale of discountinued operations	6,349	0	0	0					6,349	0	0
Net income (loss)	7,967	31,132	109,111	68,507	1,961	(566)	132,209	73,997	216,717	207,601	205,839
Income Loss From Continuing Operations Per Basic Share	$ 0.00	$ 0.31	$ 1.12	$ 0.68	$ 0.00	$ (0.04)	$ 1.36	$ 0.75	$ 2.12	$ 2.08	$ 2.05
Income Loss From Discontinued Operations Net Of Tax Per Basic Share	$ 0.09	$ 0.03	$ 0.08	$ 0.07	$ 0.02	$ 0.03	$ 0.09	$ 0.06	$ 0.27	$ 0.20	$ 0.17
Basic net income (loss) per share	$ 0.09	$ 0.34	$ 1.20	$ 0.75	$ 0.02	$ (0.01)	$ 1.45	$ 0.81	$ 2.39	$ 2.28	$ 2.22
Income Loss From Continuing Operations Per Diluted Share	$ 0.00	$ 0.31	$ 1.12	$ 0.68	$ 0.00	$ (0.04)	$ 1.36	$ 0.75	$ 2.10	$ 2.07	$ 2.03
Income Loss From Discontinued Operations Net Of Tax Per Diluted Share	$ 0.09	$ 0.03	$ 0.08	$ 0.07	$ 0.02	$ 0.03	$ 0.09	$ 0.06	$ 0.27	$ 0.20	$ 0.17
Diluted net income (loss) per share	$ 0.09	$ 0.34	$ 1.20	$ 0.75	$ 0.02	$ (0.01)	$ 1.45	$ 0.81	$ 2.37	$ 2.27	$ 2.20
Weighted average shares outstanding:
Basic									90,150	90,201	91,852
Diluted									91,172	90,652	92,422
Natural Gas Distribution Segment [Member]
Operating revenues
Operating revenues	282,516	315,634	871,067	676,113	334,363	396,584	1,052,291	687,426	2,145,330	2,470,664	2,783,863
Purchased gas cost
Purchased gas cost									1,122,587	1,452,721	1,785,221
Gross profit									1,022,743	1,017,943	998,642
Operating expenses
Operation and maintenance									353,879	341,758	349,465
Depreciation and amortization									202,026	193,642	182,097
Taxes, other than income									162,377	160,455	170,229
Asset impairments									0	0
Total operating expenses									718,282	695,855	701,791
Operating income									304,461	322,088	296,851
Miscellaneous income (expense)									(12,657)	16,242	1,132
Interest charges									110,642	115,740	118,147
Income (loss) before income taxes									181,162	222,590	179,836
Income tax expense (benefit)									57,314	77,885	69,875
Income (loss) from continuing operations									123,848	144,705	109,961
Income (loss) from discontinued operations									18,172	18,013	15,988
Gain on sale of discountinued operations									6,349
Net income (loss)									148,369	162,718	125,949
Regulated Transmission and Storage Segment [Member]
Operating revenues
Operating revenues	65,482	67,073	58,037	56,759	61,820	53,570	54,976	49,007	247,351	219,373	203,013
Purchased gas cost
Purchased gas cost									0	0	0
Gross profit									247,351	219,373	203,013
Operating expenses
Operation and maintenance									71,521	70,401	72,249
Depreciation and amortization									31,438	25,997	21,368
Taxes, other than income									15,568	14,700	12,358
Asset impairments									0	0
Total operating expenses									118,527	111,098	105,975
Operating income									128,824	108,275	97,038
Miscellaneous income (expense)									(1,051)	4,715	135
Interest charges									29,414	31,432	31,174
Income (loss) before income taxes									98,359	81,558	65,999
Income tax expense (benefit)									35,300	29,143	24,513
Income (loss) from continuing operations									63,059	52,415	41,486
Income (loss) from discontinued operations									0	0	0
Gain on sale of discountinued operations									0
Net income (loss)									63,059	52,415	41,486
Nonregulated Segment [Member]
Operating revenues
Operating revenues	280,114	256,250	370,763	444,176	474,437	491,285	583,531	475,640	1,351,303	2,024,893	2,146,658
Purchased gas cost
Purchased gas cost									1,296,179	1,959,893	2,032,567
Gross profit									55,124	65,000	114,091
Operating expenses
Operation and maintenance									29,697	32,308	34,517
Depreciation and amortization									4,061	4,193	5,074
Taxes, other than income									3,128	2,612	4,556
Asset impairments									5,288	30,270
Total operating expenses									42,174	69,383	44,147
Operating income									12,950	(4,383)	69,944
Miscellaneous income (expense)									1,035	657	3,859
Interest charges									3,084	4,015	10,584
Income (loss) before income taxes									10,901	(7,741)	63,219
Income tax expense (benefit)									5,612	(209)	24,815
Income (loss) from continuing operations									5,289	(7,532)	38,404
Income (loss) from discontinued operations									0	0	0
Gain on sale of discountinued operations									0
Net income (loss)									5,289	(7,532)	38,404
Intersegment Elimination [Member]
Operating revenues
Operating revenues	(75,546)	(62,543)	(74,358)	(93,054)	(90,953)	(108,271)	(134,424)	(94,847)	(305,501)	(428,495)	(472,474)
Purchased gas cost
Purchased gas cost									(304,022)	(426,999)	(470,864)
Gross profit									(1,479)	(1,496)	(1,610)
Operating expenses
Operation and maintenance									(1,484)	(1,502)	(1,610)
Depreciation and amortization									0	0	0
Taxes, other than income									0	0	0
Asset impairments									0	0
Total operating expenses									(1,484)	(1,502)	(1,610)
Operating income									5	6	0
Miscellaneous income (expense)									(1,971)	(430)	(5,717)
Interest charges									(1,966)	(424)	(5,717)
Income (loss) before income taxes									0	0	0
Income tax expense (benefit)									0	0	0
Income (loss) from continuing operations									0	0	0
Income (loss) from discontinued operations									0	0	0
Gain on sale of discountinued operations									0
Net income (loss)									$ 0	$ 0	$ 0