Segment Information (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2022 USD ($) state	Dec. 31, 2021 USD ($)	Sep. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of states with service areas | state	8
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	$ 1,484,009	$ 1,012,786
Purchased gas cost	738,249	371,163
Operation and maintenance expense	185,016	159,110
Depreciation and amortization expense	146,020	127,856
Taxes, other than income	93,538	78,796
Operating income	321,186	275,861
Other non-operating income	21,191	8,702
Interest charges	36,760	19,851
Income before income taxes	305,617	264,712
Income tax expense	33,757	15,503
Net income	271,860	249,209
Capital expenditures	795,660	684,180
Segment Reporting Information, Balance Sheet [Abstract]
Net property, plant and equipment	17,971,668		$ 17,240,239
Total assets	23,366,161		22,192,989
Distribution
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	1,439,693	971,636
Pipeline and Storage
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	44,316	41,150
Eliminations
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	(143,046)	(122,554)
Purchased gas cost	(142,808)	(122,225)
Operation and maintenance expense	(238)	(329)
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
Segment Reporting Information, Balance Sheet [Abstract]
Net property, plant and equipment	0		0
Total assets	(4,343,036)		(4,028,803)
Eliminations | Distribution
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	733	786
Eliminations | Pipeline and Storage
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	142,313	121,768
Operating Segments | Distribution
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	1,440,426	972,422
Purchased gas cost	881,915	496,799
Operation and maintenance expense	136,469	123,284
Depreciation and amortization expense	105,664	92,797
Taxes, other than income	84,622	69,045
Operating income	231,756	190,497
Other non-operating income	6,774	1,916
Interest charges	22,839	8,548
Income before income taxes	215,691	183,865
Income tax expense	21,223	4,294
Net income	194,468	179,571
Capital expenditures	443,544	437,382
Segment Reporting Information, Balance Sheet [Abstract]
Net property, plant and equipment	13,155,891		12,723,532
Total assets	22,595,795		21,424,586
Operating Segments | Pipeline and Storage
Segment Reporting Information Profit Loss [Abstract]
Operating revenues	186,629	162,918
Purchased gas cost	(858)	(3,411)
Operation and maintenance expense	48,785	36,155
Depreciation and amortization expense	40,356	35,059
Taxes, other than income	8,916	9,751
Operating income	89,430	85,364
Other non-operating income	14,417	6,786
Interest charges	13,921	11,303
Income before income taxes	89,926	80,847
Income tax expense	12,534	11,209
Net income	77,392	69,638
Capital expenditures	352,116	$ 246,798
Segment Reporting Information, Balance Sheet [Abstract]
Net property, plant and equipment	4,815,777		4,516,707
Total assets	$ 5,113,402		$ 4,797,206