CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Operating revenues
Operating revenues	$ 1,243,450	$ 1,581,497	$ 2,344,623	$ 2,714,759
Purchased gas cost
Purchased gas cost	809,189	1,127,829	1,547,480	1,896,367
Gross profit	434,261	453,668	797,143	818,392
Operating expenses
Operation and maintenance	110,708	114,162	226,770	228,652
Depreciation and amortization	60,272	55,467	119,487	110,244
Taxes, other than income	54,919	53,558	98,117	93,726
Asset impairments	0	19,282	0	19,282
Total operating expenses	225,899	242,469	444,374	451,904
Operating income	208,362	211,199	352,769	366,488
Miscellaneous income (expense)	616	26,202	(1,259)	25,476
Interest charges	36,660	37,875	72,102	76,770
Income (loss) before income taxes	172,318	199,526	279,408	315,194
Income tax expense (benefit)	66,408	71,366	107,710	115,934
Income (loss) from continuing operations	105,910	128,160	171,698	199,260
Discontinued Operation Income Loss From Discontinued Operation During Phase Out Period Net Of Tax	3,201	4,049	5,920	6,946
Net income (loss)	109,111	132,209	177,618	206,206
Income Loss From Continuing Operations Per Basic Share	$ 1.16	$ 1.41	$ 1.89	$ 2.18
Income Loss From Discontinued Operations Net Of Tax Per Basic Share	$ 0.04	$ 0.04	$ 0.06	$ 0.08
Basic net income (loss) per share	$ 1.20	$ 1.45	$ 1.95	$ 2.26
Income Loss From Continuing Operations Per Diluted Share	$ 1.16	$ 1.41	$ 1.88	$ 2.18
Income Loss From Discontinued Operations Net Of Tax Per Diluted Share	$ 0.04	$ 0.04	$ 0.06	$ 0.08
Diluted net income (loss) per share	$ 1.20	$ 1.45	$ 1.94	$ 2.26
Cash dividends per share	$ 0.345	$ 0.340	$ 0.690	$ 0.680
Weighted average shares outstanding:
Basic	90,020	90,246	90,137	90,157
Diluted	90,322	90,533	90,440	90,455
Natural Gas Distribution Segment [Member]
Operating revenues
Operating revenues	889,008	1,077,414	1,582,300	1,780,876
Purchased gas cost
Purchased gas cost	508,206	698,410	910,413	1,110,936
Gross profit	380,802	379,004	671,887	669,940
Operating expenses
Operation and maintenance	89,443	92,266	182,857	181,495
Depreciation and amortization	51,755	48,555	102,586	96,449
Taxes, other than income	50,313	50,088	88,792	84,536
Asset impairments	0	0	0	0
Total operating expenses	191,511	190,909	374,235	362,480
Operating income	189,291	188,095	297,652	307,460
Miscellaneous income (expense)	733	20,156	(1,023)	19,458
Interest charges	28,833	29,605	56,688	59,302
Income (loss) before income taxes	161,191	178,646	239,941	267,616
Income tax expense (benefit)	62,890	64,085	93,735	98,634
Income (loss) from continuing operations	98,301	114,561	146,206	168,982
Discontinued Operation Income Loss From Discontinued Operation During Phase Out Period Net Of Tax	3,201	4,049	5,920	6,946
Net income (loss)	101,502	118,610	152,126	175,928
Regulated Transmission and Storage Segment [Member]
Operating revenues
Operating revenues	58,037	54,976	114,796	103,983
Purchased gas cost
Purchased gas cost	0	0	0	0
Gross profit	58,037	54,976	114,796	103,983
Operating expenses
Operation and maintenance	15,847	15,231	32,812	30,805
Depreciation and amortization	7,792	5,798	15,443	11,597
Taxes, other than income	3,915	4,113	7,699	7,666
Asset impairments	0	0	0	0
Total operating expenses	27,554	25,142	55,954	50,068
Operating income	30,483	29,834	58,842	53,915
Miscellaneous income (expense)	(56)	5,861	(336)	5,579
Interest charges	7,614	8,085	14,823	16,149
Income (loss) before income taxes	22,813	27,610	43,683	43,345
Income tax expense (benefit)	8,193	9,871	15,649	15,504
Income (loss) from continuing operations	14,620	17,739	28,034	27,841
Discontinued Operation Income Loss From Discontinued Operation During Phase Out Period Net Of Tax	0	0	0	0
Net income (loss)	14,620	17,739	28,034	27,841
Nonregulated Segment [Member]
Operating revenues
Operating revenues	370,763	583,531	814,939	1,059,171
Purchased gas cost
Purchased gas cost	374,992	563,473	803,763	1,013,935
Gross profit	(4,229)	20,058	11,176	45,236
Operating expenses
Operation and maintenance	5,769	7,035	11,820	17,119
Depreciation and amortization	725	1,114	1,458	2,198
Taxes, other than income	691	(643)	1,626	1,524
Asset impairments	0	19,282	0	19,282
Total operating expenses	7,185	26,788	14,904	40,123
Operating income	(11,414)	(6,730)	(3,728)	5,113
Miscellaneous income (expense)	567	306	603	596
Interest charges	839	306	1,091	1,476
Income (loss) before income taxes	(11,686)	(6,730)	(4,216)	4,233
Income tax expense (benefit)	(4,675)	(2,590)	(1,674)	1,796
Income (loss) from continuing operations	(7,011)	(4,140)	(2,542)	2,437
Discontinued Operation Income Loss From Discontinued Operation During Phase Out Period Net Of Tax	0	0	0	0
Net income (loss)	(7,011)	(4,140)	(2,542)	2,437
Intersegment Elimination [Member]
Operating revenues
Operating revenues	(74,358)	(134,424)	(167,412)	(229,271)
Purchased gas cost
Purchased gas cost	(74,009)	(134,054)	(166,696)	(228,504)
Gross profit	(349)	(370)	(716)	(767)
Operating expenses
Operation and maintenance	(351)	(370)	(719)	(767)
Depreciation and amortization	0	0	0	0
Taxes, other than income	0	0	0	0
Asset impairments	0	0	0	0
Total operating expenses	(351)	(370)	(719)	(767)
Operating income	2	0	3	0
Miscellaneous income (expense)	(628)	(121)	(503)	(157)
Interest charges	(626)	(121)	(500)	(157)
Income (loss) before income taxes	0	0	0	0
Income tax expense (benefit)	0	0	0	0
Income (loss) from continuing operations	0	0	0	0
Discontinued Operation Income Loss From Discontinued Operation During Phase Out Period Net Of Tax	0	0	0	0
Net income (loss)	$ 0	$ 0	$ 0	$ 0