CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Operating revenues	$ 4,702,755	$ 4,165,187	$ 4,275,357
Purchased gas cost	1,066,054	933,693	1,452,173
Operation and maintenance expense	902,942	819,137	764,906
Depreciation and amortization expense	734,745	669,972	604,327
Taxes, other than income	439,043	387,023	386,804
Operating income	1,559,971	1,355,362	1,067,147
Other non-operating income	89,741	71,046	69,775
Interest charges	171,678	190,632	137,281
Income before income taxes	1,478,034	1,235,776	999,641
Income tax expense	279,280	192,881	113,779
Net income	$ 1,198,754	$ 1,042,895	$ 885,862
Basic net income per share (USD per share)	$ 7.54	$ 6.83	$ 6.10
Diluted net income per share (USD per share)	$ 7.46	$ 6.83	$ 6.10
Weighted average shares outstanding:
Basic (in shares)	158,943	152,508	145,121
Diluted (in shares)	160,573	152,666	145,166
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax of $(3), $168 and $37	$ (4)	$ 582	$ 126
Cash flow hedges:
Amortization and unrealized gains (losses) on interest rate agreements, net of tax of $1,103, $(15,432) and $43,148	9,304	(53,395)	149,290
Total other comprehensive income (loss)	9,300	(52,813)	149,416
Total comprehensive income	1,208,054	990,082	1,035,278
Distribution segment
Operating revenues	4,422,355	3,912,134	4,096,661
Depreciation and amortization expense	543,840	491,982	434,721
Interest charges	99,226	117,086	77,185
Income tax expense	150,961	96,041	60,032
Net income	746,781	671,413	580,397
Pipeline and storage segment
Operating revenues	280,400	253,053	178,696
Depreciation and amortization expense	190,905	177,990	169,606
Interest charges	72,452	73,546	60,096
Income tax expense	128,319	96,840	53,747
Net income	451,973	371,482	305,465
Operating Segments
Operating revenues	5,490,697	4,853,170	4,884,864
Operating Segments | Distribution segment
Operating revenues	4,425,397	3,915,141	4,099,690
Purchased gas cost	1,854,323	1,620,515	2,061,920
Operating Segments | Pipeline and storage segment
Operating revenues	1,065,300	938,029	785,174
Purchased gas cost	(1,346)	146	(1,220)
Intersegment eliminations
Operating revenues	(787,942)	(687,983)	(609,507)
Purchased gas cost	(786,923)	(686,968)	(608,527)
Intersegment eliminations | Distribution segment
Operating revenues	(3,042)	(3,007)	(3,029)
Intersegment eliminations | Pipeline and storage segment
Operating revenues	$ (784,900)	$ (684,976)	$ (606,478)