CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating revenues
Operating revenues	$ 632,916	$ 686,401	$ 2,671,430	$ 3,485,234
Purchased gas cost
Purchased gas cost	225,605	304,728	1,302,545	2,159,538
Gross profit	407,311	381,673	1,368,885	1,325,696
Operating expenses
Operation and maintenance	137,444	132,447	395,958	384,489
Depreciation and amortization	73,459	68,444	216,670	204,059
Taxes, other than income	59,244	63,175	172,872	181,606
Total operating expenses	270,147	264,066	785,500	770,154
Operating income	137,164	117,607	583,385	555,542
Miscellaneous income (expense)	833	634	(1,061)	(2,634)
Interest charges	27,698	27,955	85,741	85,166
Income (loss) before income taxes	110,299	90,286	496,583	467,742
Income tax expense (benefit)	39,106	34,005	180,719	176,182
Net income (loss)	$ 71,193	$ 56,281	$ 315,864	$ 291,560
Basic and diluted net income per share	$ 0.69	$ 0.55	$ 3.06	$ 2.86
Cash dividends per share	$ 0.42	$ 0.39	$ 1.26	$ 1.17
Weighted average shares outstanding:
Weighted Average Number of Shares Outstanding, Basic and Diluted	103,750	102,000	103,137	101,776
Regulated Distribution Segment [Member]
Operating revenues
Operating revenues	$ 414,226	$ 416,794	$ 1,902,513	$ 2,394,179
Purchased gas cost
Purchased gas cost	138,845	149,775	884,529	1,397,113
Gross profit	275,381	267,019	1,017,984	997,066
Operating expenses
Operation and maintenance	100,859	98,552	291,388	288,962
Depreciation and amortization	58,916	55,491	173,913	165,730
Taxes, other than income	52,377	56,176	152,324	162,759
Total operating expenses	212,152	210,219	617,625	617,451
Operating income	63,229	56,800	400,359	379,615
Miscellaneous income (expense)	1,111	1,045	209	(1,221)
Interest charges	18,968	19,961	58,390	60,914
Income (loss) before income taxes	45,372	37,884	342,178	317,480
Income tax expense (benefit)	15,516	15,420	124,755	121,776
Net income (loss)	29,856	22,464	217,423	195,704
Regulated Pipeline Segment [Member]
Operating revenues
Operating revenues	109,249	97,008	299,629	272,305
Purchased gas cost
Purchased gas cost	0	0	0	0
Gross profit	109,249	97,008	299,629	272,305
Operating expenses
Operation and maintenance	29,083	26,572	83,302	74,029
Depreciation and amortization	13,409	11,816	39,358	34,945
Taxes, other than income	6,220	6,193	18,529	16,296
Total operating expenses	48,712	44,581	141,189	125,270
Operating income	60,537	52,427	158,440	147,035
Miscellaneous income (expense)	(359)	(211)	(1,164)	(842)
Interest charges	9,002	8,299	27,294	25,014
Income (loss) before income taxes	51,176	43,917	129,982	121,179
Income tax expense (benefit)	18,046	15,349	46,081	42,894
Net income (loss)	33,130	28,568	83,901	78,285
Nonregulated Segment [Member]
Operating revenues
Operating revenues	214,555	278,769	774,474	1,179,379
Purchased gas cost
Purchased gas cost	191,741	260,990	722,803	1,122,655
Gross profit	22,814	17,779	51,671	56,724
Operating expenses
Operation and maintenance	7,635	7,456	21,667	21,897
Depreciation and amortization	1,134	1,137	3,399	3,384
Taxes, other than income	647	806	2,019	2,551
Total operating expenses	9,416	9,399	27,085	27,832
Operating income	13,398	8,380	24,586	28,892
Miscellaneous income (expense)	574	345	1,245	897
Interest charges	221	240	1,408	706
Income (loss) before income taxes	13,751	8,485	24,423	29,083
Income tax expense (benefit)	5,544	3,236	9,883	11,512
Net income (loss)	8,207	5,249	14,540	17,571
Intersegment Elimination [Member]
Operating revenues
Operating revenues	(105,114)	(106,170)	(305,186)	(360,629)
Purchased gas cost
Purchased gas cost	(104,981)	(106,037)	(304,787)	(360,230)
Gross profit	(133)	(133)	(399)	(399)
Operating expenses
Operation and maintenance	(133)	(133)	(399)	(399)
Depreciation and amortization	0	0	0	0
Taxes, other than income	0	0	0	0
Total operating expenses	(133)	(133)	(399)	(399)
Operating income	0	0	0	0
Miscellaneous income (expense)	(493)	(545)	(1,351)	(1,468)
Interest charges	(493)	(545)	(1,351)	(1,468)
Income (loss) before income taxes	0	0	0	0
Income tax expense (benefit)	0	0	0	0
Net income (loss)	$ 0	$ 0	$ 0	$ 0