CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Operating revenues	$ 4,165,187	$ 4,275,357	$ 4,201,662
Purchased gas cost	933,693	1,452,173	1,682,656
Operation and maintenance expense	819,137	764,906	710,161
Depreciation and amortization expense	669,972	604,327	535,655
Taxes, other than income	387,023	386,804	352,208
Operating income	1,355,362	1,067,147	920,982
Other non-operating income	71,046	69,775	33,737
Interest charges	190,632	137,281	102,811
Income before income taxes	1,235,776	999,641	851,908
Income tax expense	192,881	113,779	77,510
Net income	$ 1,042,895	$ 885,862	$ 774,398
Basic net income per share (USD per share)	$ 6.83	$ 6.10	$ 5.61
Diluted net income per share (USD per share)	$ 6.83	$ 6.10	$ 5.60
Weighted average shares outstanding:
Basic (in shares)	152,508	145,121	137,830
Diluted (in shares)	152,666	145,166	138,096
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax of $168, $37 and $(157)	$ 582	$ 126	$ (542)
Cash flow hedges:
Amortization and unrealized gains (losses) on interest rate agreements, net of tax of $(15,432), $43,148 and $86,664	(53,395)	149,290	299,851
Total other comprehensive income (loss)	(52,813)	149,416	299,309
Total comprehensive income	990,082	1,035,278	1,073,707
Distribution segment
Operating revenues	3,912,134	4,096,661	4,031,936
Pipeline and storage segment
Operating revenues	253,053	178,696	169,726
Operating Segments | Distribution segment
Operating revenues	3,915,141	4,099,690	4,035,194
Purchased gas cost	1,620,515	2,061,920	2,210,302
Operation and maintenance expense	601,370	565,179	518,443
Depreciation and amortization expense	491,982	434,721	387,858
Taxes, other than income	346,840	345,244	314,046
Operating income	854,434	692,626	604,545
Other non-operating income	30,106	24,988	6,946
Interest charges	117,086	77,185	49,921
Income before income taxes	767,454	640,429	561,570
Income tax expense	96,041	60,032	39,593
Net income	671,413	580,397	521,977
Operating Segments | Pipeline and storage segment
Operating revenues	938,029	785,174	693,660
Purchased gas cost	146	(1,220)	(1,583)
Operation and maintenance expense	218,782	200,707	192,847
Depreciation and amortization expense	177,990	169,606	147,797
Taxes, other than income	40,183	41,560	38,162
Operating income	500,928	374,521	316,437
Other non-operating income	40,940	44,787	26,791
Interest charges	73,546	60,096	52,890
Income before income taxes	468,322	359,212	290,338
Income tax expense	96,840	53,747	37,917
Net income	371,482	305,465	252,421
Intersegment eliminations
Operating revenues	(687,983)	(609,507)	(527,192)
Purchased gas cost	(686,968)	(608,527)	(526,063)
Operation and maintenance expense	(1,015)	(980)	(1,129)
Depreciation and amortization expense	0	0	0
Taxes, other than income	0	0	0
Operating income	0	0	0
Other non-operating income	0	0	0
Interest charges	0	0	0
Income before income taxes	0	0	0
Income tax expense	0	0	0
Net income	0	0	0
Intersegment eliminations | Distribution segment
Operating revenues	(3,007)	(3,029)	(3,258)
Intersegment eliminations | Pipeline and storage segment
Operating revenues	$ (684,976)	$ (606,478)	$ (523,934)