CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Operating revenues
Operating revenues	$ 906,221	$ 1,258,765
Purchased gas cost
Purchased gas cost	462,458	835,480
Gross profit	443,763	423,285
Operating expenses
Operation and maintenance	124,848	118,582
Depreciation and amortization	71,239	67,593
Taxes, other than income	51,471	49,385
Total operating expenses	247,558	235,560
Operating income	196,205	187,725
Miscellaneous income (expense)	(1,209)	(1,707)
Interest charges	30,483	29,764
Income (loss) before income taxes	164,513	156,254
Income tax expense (benefit)	61,652	58,659
Net income (loss)	$ 102,861	$ 97,595
Basic and diluted net income per share	$ 1.00	$ 0.96
Cash dividends per share	$ 0.42	$ 0.39
Weighted average shares outstanding:
Weighted Average Number of Shares Outstanding, Basic and Diluted	102,713	101,581
Regulated Distribution Segment [Member]
Operating revenues
Operating revenues	$ 638,602	$ 846,772
Purchased gas cost
Purchased gas cost	305,141	522,960
Gross profit	333,461	323,812
Operating expenses
Operation and maintenance	91,349	86,985
Depreciation and amortization	57,334	55,086
Taxes, other than income	45,261	43,644
Total operating expenses	193,944	185,715
Operating income	139,517	138,097
Miscellaneous income (expense)	(752)	(1,329)
Interest charges	20,705	21,640
Income (loss) before income taxes	118,060	115,128
Income tax expense (benefit)	44,805	43,741
Net income (loss)	73,255	71,387
Regulated Pipeline Segment [Member]
Operating revenues
Operating revenues	94,677	83,567
Purchased gas cost
Purchased gas cost	0	0
Gross profit	94,677	83,567
Operating expenses
Operation and maintenance	27,088	24,615
Depreciation and amortization	12,770	11,382
Taxes, other than income	5,571	4,865
Total operating expenses	45,429	40,862
Operating income	49,248	42,705
Miscellaneous income (expense)	(429)	(252)
Interest charges	9,147	8,324
Income (loss) before income taxes	39,672	34,129
Income tax expense (benefit)	14,086	12,094
Net income (loss)	25,586	22,035
Nonregulated Segment [Member]
Operating revenues
Operating revenues	272,524	462,288
Purchased gas cost
Purchased gas cost	256,766	446,249
Gross profit	15,758	16,039
Operating expenses
Operation and maintenance	6,544	7,115
Depreciation and amortization	1,135	1,125
Taxes, other than income	639	876
Total operating expenses	8,318	9,116
Operating income	7,440	6,923
Miscellaneous income (expense)	379	300
Interest charges	1,038	226
Income (loss) before income taxes	6,781	6,997
Income tax expense (benefit)	2,761	2,824
Net income (loss)	4,020	4,173
Intersegment Elimination [Member]
Operating revenues
Operating revenues	(99,582)	(133,862)
Purchased gas cost
Purchased gas cost	(99,449)	(133,729)
Gross profit	(133)	(133)
Operating expenses
Operation and maintenance	(133)	(133)
Depreciation and amortization	0	0
Taxes, other than income	0	0
Total operating expenses	(133)	(133)
Operating income	0	0
Miscellaneous income (expense)	(407)	(426)
Interest charges	(407)	(426)
Income (loss) before income taxes	0	0
Income tax expense (benefit)	0	0
Net income (loss)	$ 0	$ 0