Segment Information - Schedule of Income Statements and Capital Expenditures By Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Operating revenues	$ 1,158,467	$ 1,484,009
Purchased gas cost	338,869	738,249
Operation and maintenance expense	166,345	185,016
Depreciation and amortization expense	164,608	146,020
Taxes, other than income	89,540	93,538
Operating income	399,105	321,186
Other non-operating income	17,886	21,191
Interest charges	51,875	36,760
Income before income taxes	365,116	305,617
Income tax expense	53,824	33,757
Net income	311,292	271,860
Capital expenditures	769,650	795,660
Distribution segment
Segment Reporting Information [Line Items]
Operating revenues	1,104,619	1,439,693
Pipeline and storage segment
Segment Reporting Information [Line Items]
Operating revenues	53,848	44,316
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(158,040)	(143,046)
Purchased gas cost	(157,797)	(142,808)
Operation and maintenance expense	(243)	(238)
Depreciation and amortization expense	0	0
Taxes, other than income	0	0
Operating income	0	0
Other non-operating income	0	0
Interest charges	0	0
Income before income taxes	0	0
Income tax expense	0	0
Net income	0	0
Capital expenditures	0	0
Eliminations | Distribution segment
Segment Reporting Information [Line Items]
Operating revenues	719	733
Eliminations | Pipeline and storage segment
Segment Reporting Information [Line Items]
Operating revenues	157,321	142,313
Operating Segments | Distribution segment
Segment Reporting Information [Line Items]
Operating revenues	1,105,338	1,440,426
Purchased gas cost	496,662	881,915
Operation and maintenance expense	127,615	136,469
Depreciation and amortization expense	119,685	105,664
Taxes, other than income	80,895	84,622
Operating income	280,481	231,756
Other non-operating income	5,839	6,774
Interest charges	34,581	22,839
Income before income taxes	251,739	215,691
Income tax expense	30,302	21,223
Net income	221,437	194,468
Capital expenditures	539,158	443,544
Operating Segments | Pipeline and storage segment
Segment Reporting Information [Line Items]
Operating revenues	211,169	186,629
Purchased gas cost	4	(858)
Operation and maintenance expense	38,973	48,785
Depreciation and amortization expense	44,923	40,356
Taxes, other than income	8,645	8,916
Operating income	118,624	89,430
Other non-operating income	12,047	14,417
Interest charges	17,294	13,921
Income before income taxes	113,377	89,926
Income tax expense	23,522	12,534
Net income	89,855	77,392
Capital expenditures	$ 230,492	$ 352,116