CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Operating revenues	$ 1,950,502	$ 1,647,227	$ 3,126,501	$ 2,805,694
Purchased gas cost	779,233	624,295	1,013,281	963,164
Operation and maintenance expense	233,296	199,899	440,340	366,244
Depreciation and amortization expense	182,750	165,087	363,283	329,695
Taxes, other than income	126,284	106,956	221,178	196,496
Operating income	628,939	550,990	1,088,419	950,095
Other non-operating income	24,172	16,687	48,806	34,573
Interest charges	50,014	55,442	102,939	107,317
Income before income taxes	603,097	512,235	1,034,286	877,351
Income tax expense	117,521	80,212	196,852	134,036
Net income	$ 485,576	$ 432,023	$ 837,434	$ 743,315
Basic net income per share (USD per share)	$ 3.05	$ 2.85	$ 5.31	$ 4.93
Diluted net income per share (USD per share)	3.03	2.85	5.26	4.93
Cash dividends per share (USD per share)	$ 0.870	$ 0.805	$ 1.74	$ 1.61
Basic weighted average shares outstanding (in shares)	159,177	151,271	157,739	150,534
Diluted weighted average shares outstanding (in shares)	160,426	151,297	159,125	150,547
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax of $20 and $(15)	$ 73	$ (50)	$ (65)	$ 246
Cash flow hedges:
Amortization and unrealized gains (losses) on interest rate agreements, net of tax of $(1,622) and $7,850	(5,660)	27,158	10,901	(23,074)
Total other comprehensive income (loss)	(5,587)	27,108	10,836	(22,828)
Total comprehensive income	479,989	459,131	848,270	720,487
Distribution segment
Operating revenues	1,881,742	1,588,394	2,990,311	2,693,013
Pipeline and storage segment
Operating revenues	68,760	58,833	136,190	112,681
Operating Segments | Distribution segment
Operating revenues	1,882,528	1,589,181	2,991,863	2,694,519
Purchased gas cost	969,037	788,643	1,391,607	1,285,305
Operation and maintenance expense	181,887	154,956	336,401	282,571
Depreciation and amortization expense	134,546	121,384	268,173	241,069
Taxes, other than income	113,340	98,008	195,916	178,903
Operating income	483,718	426,190	799,766	706,671
Other non-operating income	13,444	9,359	23,528	15,198
Interest charges	30,087	36,784	64,336	71,365
Income before income taxes	467,075	398,765	758,958	650,504
Income tax expense	86,432	56,073	138,102	86,375
Net income	380,643	342,692	620,856	564,129
Operating Segments | Pipeline and storage segment
Operating revenues	258,999	223,487	514,389	434,656
Purchased gas cost	968	840	910	844
Operation and maintenance expense	51,662	45,196	104,454	84,169
Depreciation and amortization expense	48,204	43,703	95,110	88,626
Taxes, other than income	12,944	8,948	25,262	17,593
Operating income	145,221	124,800	288,653	243,424
Other non-operating income	10,728	7,328	25,278	19,375
Interest charges	19,927	18,658	38,603	35,952
Income before income taxes	136,022	113,470	275,328	226,847
Income tax expense	31,089	24,139	58,750	47,661
Net income	104,933	89,331	216,578	179,186
Eliminations
Operating revenues	(191,025)	(165,441)	(379,751)	(323,481)
Purchased gas cost	(190,772)	(165,188)	(379,236)	(322,985)
Operation and maintenance expense	(253)	(253)	(515)	(496)
Depreciation and amortization expense	0	0	0	0
Taxes, other than income	0	0	0	0
Operating income	0	0	0	0
Other non-operating income	0	0	0	0
Interest charges	0	0	0	0
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Eliminations | Distribution segment
Operating revenues	(786)	(787)	(1,552)	(1,506)
Eliminations | Pipeline and storage segment
Operating revenues	$ (190,239)	$ (164,654)	$ (378,199)	$ (321,975)