CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Operating revenues
Operating revenues	$ 1,255,148,000	$ 1,034,155,000
Purchased gas cost
Purchased gas cost	866,191,000	671,793,000
Gross profit	388,957,000	362,362,000
Operating expenses
Operation and maintenance	115,757,000	106,527,000
Depreciation and amortization	60,469,000	59,579,000
Taxes, other than income	42,011,000	41,334,000
Total operating expenses	218,237,000	207,440,000
Operating income	170,720,000	154,922,000
Miscellaneous income (expense)	(2,132,000)	698,000
Interest charges	32,115,000	30,522,000
Income (loss) before income taxes	136,473,000	125,098,000
Income tax expense (benefit)	49,457,000	47,750,000
Income (loss) from continuing operations	87,016,000	77,348,000
Income from discontinued operations, net of tax	0	3,117,000
Net income (loss)	87,016,000	80,465,000
Income Loss From Continuing Operations Per Basic Share	$ 0.96	$ 0.85
Income Loss From Discontinued Operations Net Of Tax Per Basic Share	$ 0.00	$ 0.04
Basic net income (loss) per share	$ 0.96	$ 0.89
Income Loss From Continuing Operations Per Diluted Share	$ 0.95	$ 0.85
Income Loss From Discontinued Operations Net Of Tax Per Diluted Share	$ 0.00	$ 0.03
Diluted net income (loss) per share	$ 0.95	$ 0.88
Cash dividends per share	$ 0.37	$ 0.35
Weighted average shares outstanding:
Basic weighted average shares outstanding	90,833	90,359
Diluted weighted average shares outstanding	91,746	91,309
Natural Gas Distribution Segment [Member]
Operating revenues
Operating revenues	843,865,000	666,787,000
Purchased gas cost
Purchased gas cost	544,694,000	387,156,000
Gross profit	299,171,000	279,631,000
Operating expenses
Operation and maintenance	89,663,000	83,736,000
Depreciation and amortization	49,551,000	50,060,000
Taxes, other than income	37,084,000	36,751,000
Total operating expenses	176,298,000	170,547,000
Operating income	122,873,000	109,084,000
Miscellaneous income (expense)	(471,000)	(131,000)
Interest charges	23,325,000	23,563,000
Income (loss) before income taxes	99,077,000	85,390,000
Income tax expense (benefit)	36,320,000	32,297,000
Income (loss) from continuing operations		53,093,000
Income from discontinued operations, net of tax		3,117,000
Net income (loss)	62,757,000	56,210,000
Regulated Transmission and Storage Segment [Member]
Operating revenues
Operating revenues	71,341,000	60,681,000
Purchased gas cost
Purchased gas cost	0	0
Gross profit	71,341,000	60,681,000
Operating expenses
Operation and maintenance	17,300,000	16,320,000
Depreciation and amortization	9,786,000	8,390,000
Taxes, other than income	4,663,000	3,949,000
Total operating expenses	31,749,000	28,659,000
Operating income	39,592,000	32,022,000
Miscellaneous income (expense)	(1,181,000)	(127,000)
Interest charges	8,957,000	6,871,000
Income (loss) before income taxes	29,454,000	25,024,000
Income tax expense (benefit)	10,008,000	8,919,000
Income (loss) from continuing operations		16,105,000
Income from discontinued operations, net of tax		0
Net income (loss)	19,446,000	16,105,000
Nonregulated Segment [Member]
Operating revenues
Operating revenues	447,721,000	399,894,000
Purchased gas cost
Purchased gas cost	429,155,000	377,435,000
Gross profit	18,566,000	22,459,000
Operating expenses
Operation and maintenance	8,915,000	6,882,000
Depreciation and amortization	1,132,000	1,129,000
Taxes, other than income	264,000	634,000
Total operating expenses	10,311,000	8,645,000
Operating income	8,255,000	13,814,000
Miscellaneous income (expense)	324,000	1,667,000
Interest charges	637,000	797,000
Income (loss) before income taxes	7,942,000	14,684,000
Income tax expense (benefit)	3,129,000	6,534,000
Income (loss) from continuing operations		8,150,000
Income from discontinued operations, net of tax		0
Net income (loss)	4,813,000	8,150,000
Intersegment Elimination [Member]
Operating revenues
Operating revenues	(107,779,000)	(93,207,000)
Purchased gas cost
Purchased gas cost	(107,658,000)	(92,798,000)
Gross profit	(121,000)	(409,000)
Operating expenses
Operation and maintenance	(121,000)	(411,000)
Depreciation and amortization	0	0
Taxes, other than income	0	0
Total operating expenses	(121,000)	(411,000)
Operating income	0	2,000
Miscellaneous income (expense)	(804,000)	(711,000)
Interest charges	(804,000)	(709,000)
Income (loss) before income taxes	0	0
Income tax expense (benefit)	0	0
Income (loss) from continuing operations		0
Income from discontinued operations, net of tax		0
Net income (loss)	$ 0	$ 0