CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Operating revenues
Operating revenues	$ 1,540,068	$ 1,964,854	$ 2,798,833	$ 3,208,712
Purchased gas cost
Purchased gas cost	1,019,330	1,468,577	1,854,810	2,323,478
Gross profit	520,738	496,277	944,023	885,234
Operating expenses
Operation and maintenance	133,460	124,675	252,042	240,432
Depreciation and amortization	68,022	61,307	135,615	121,776
Taxes, other than income	69,046	60,215	118,431	102,226
Total operating expenses	270,528	246,197	506,088	464,434
Operating income	250,210	250,080	437,935	420,800
Miscellaneous income (expense)	(1,561)	(1,516)	(3,268)	(3,648)
Interest charges	27,447	31,601	57,211	63,716
Income (loss) before income taxes	221,202	216,963	377,456	353,436
Income tax expense (benefit)	83,518	83,596	142,177	133,053
Net income (loss)	137,684	133,367	235,279	220,383
Basic net income (loss) per share	$ 1.35	$ 1.38	$ 2.31	$ 2.34
Diluted net income (loss) per share	$ 1.35	$ 1.38	$ 2.31	$ 2.34
Cash dividends per share	$ 0.39	$ 0.37	$ 0.78	$ 0.74
Weighted average shares outstanding:
Basic weighted average shares outstanding	101,746	96,174	101,667	94,013
Diluted weighted average shares outstanding	101,746	96,176	101,667	94,015
Regulated Distribution Segment [Member]
Operating revenues
Operating revenues	1,130,613	1,290,960	1,977,385	2,134,825
Purchased gas cost
Purchased gas cost	724,378	905,772	1,247,338	1,450,466
Gross profit	406,235	385,188	730,047	684,359
Operating expenses
Operation and maintenance	103,425	106,776	190,410	196,439
Depreciation and amortization	55,153	50,020	110,239	99,571
Taxes, other than income	62,939	60,606	106,583	97,690
Total operating expenses	221,517	217,402	407,232	393,700
Operating income	184,718	167,786	322,815	290,659
Miscellaneous income (expense)	(937)	97	(2,266)	(374)
Interest charges	19,313	22,828	40,953	46,153
Income (loss) before income taxes	164,468	145,055	279,596	244,132
Income tax expense (benefit)	62,615	56,312	106,356	92,632
Net income (loss)	101,853	88,743	173,240	151,500
Regulated Pipeline Segment [Member]
Operating revenues
Operating revenues	91,730	73,615	175,297	144,956
Purchased gas cost
Purchased gas cost	0	0	0	0
Gross profit	91,730	73,615	175,297	144,956
Operating expenses
Operation and maintenance	22,842	16,595	47,457	33,895
Depreciation and amortization	11,747	10,156	23,129	19,942
Taxes, other than income	5,238	(1,232)	10,103	3,431
Total operating expenses	39,827	25,519	80,689	57,268
Operating income	51,903	48,096	94,608	87,688
Miscellaneous income (expense)	(379)	(1,081)	(631)	(2,262)
Interest charges	8,391	9,155	16,715	18,112
Income (loss) before income taxes	43,133	37,860	77,262	67,314
Income tax expense (benefit)	15,451	13,751	27,545	23,759
Net income (loss)	27,682	24,109	49,717	43,555
Nonregulated Segment [Member]
Operating revenues
Operating revenues	438,322	758,215	900,610	1,194,646
Purchased gas cost
Purchased gas cost	415,416	720,626	861,665	1,138,491
Gross profit	22,906	37,589	38,945	56,155
Operating expenses
Operation and maintenance	7,326	1,419	14,441	10,334
Depreciation and amortization	1,122	1,131	2,247	2,263
Taxes, other than income	869	841	1,745	1,105
Total operating expenses	9,317	3,391	18,433	13,702
Operating income	13,589	34,198	20,512	42,453
Miscellaneous income (expense)	252	443	552	767
Interest charges	240	593	466	1,230
Income (loss) before income taxes	13,601	34,048	20,598	41,990
Income tax expense (benefit)	5,452	13,533	8,276	16,662
Net income (loss)	8,149	20,515	12,322	25,328
Intersegment Elimination [Member]
Operating revenues
Operating revenues	(120,597)	(157,936)	(254,459)	(265,715)
Purchased gas cost
Purchased gas cost	(120,464)	(157,821)	(254,193)	(265,479)
Gross profit	(133)	(115)	(266)	(236)
Operating expenses
Operation and maintenance	(133)	(115)	(266)	(236)
Depreciation and amortization	0	0	0	0
Taxes, other than income	0	0	0	0
Total operating expenses	(133)	(115)	(266)	(236)
Operating income	0	0	0	0
Miscellaneous income (expense)	(497)	(975)	(923)	(1,779)
Interest charges	(497)	(975)	(923)	(1,779)
Income (loss) before income taxes	0	0	0	0
Income tax expense (benefit)	0	0	0	0
Net income (loss)	$ 0	$ 0	$ 0	$ 0