CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Operating revenues	$ 1,540,973	$ 1,649,819	$ 3,024,982	$ 2,662,605
Purchased gas cost	666,211	871,378	1,404,460	1,242,541
Operation and maintenance expense	194,716	163,352	379,732	322,462
Depreciation and amortization expense	148,317	133,374	294,337	261,230
Taxes, other than income	109,091	96,583	202,629	175,379
Operating income	422,638	385,132	743,824	660,993
Other non-operating income	17,406	5,213	38,597	13,915
Interest charges	37,370	28,928	74,130	48,779
Income before income taxes	402,674	361,417	708,291	626,129
Income tax expense	45,003	36,418	78,760	51,921
Net income	$ 357,671	$ 324,999	$ 629,531	$ 574,208
Basic net income per share (USD per share)	$ 2.48	$ 2.37	$ 4.40	$ 4.24
Diluted net income per share (USD per share)	2.48	2.37	4.40	4.24
Cash dividends per share (USD per share)	$ 0.74	$ 0.68	$ 1.48	$ 1.36
Basic weighted average shares outstanding (in shares)	143,941	136,834	142,881	135,259
Diluted weighted average shares outstanding (in shares)	143,987	137,250	142,963	135,470
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities	$ 134	$ (161)	$ 221	$ (230)
Cash flow hedges:
Amortization and unrealized gains (losses) on interest rate agreements	(30,467)	121,884	(8,336)	76,006
Total other comprehensive income (loss)	(30,333)	121,723	(8,115)	75,776
Total comprehensive income	327,338	446,722	621,416	649,984
Distribution segment
Operating revenues	1,499,437	1,609,667	2,939,130	2,581,303
Pipeline and storage segment
Operating revenues	41,536	40,152	85,852	81,302
Purchased gas cost
Purchased gas cost	666,211	871,378	1,404,460	1,242,541
Operating Segments | Distribution segment
Operating revenues	1,500,210	1,610,546	2,940,636	2,582,968
Purchased gas cost	809,023	993,854	1,690,938	1,490,653
Operation and maintenance expense	151,353	121,541	287,822	244,825
Depreciation and amortization expense	106,310	96,612	211,974	189,409
Taxes, other than income	98,200	87,236	182,822	156,281
Operating income	335,324	311,303	567,080	501,800
Other non-operating income	7,465	549	14,239	2,465
Interest charges	21,420	15,157	44,259	23,705
Income before income taxes	321,369	296,695	537,060	480,560
Income tax expense	32,895	27,844	54,118	32,138
Net income	288,474	268,851	482,942	448,422
Operating Segments | Pipeline and storage segment
Operating revenues	184,424	163,747	371,053	326,665
Purchased gas cost	621	1,683	(237)	(1,728)
Operation and maintenance expense	43,591	42,126	92,376	78,281
Depreciation and amortization expense	42,007	36,762	82,363	71,821
Taxes, other than income	10,891	9,347	19,807	19,098
Operating income	87,314	73,829	176,744	159,193
Other non-operating income	9,941	4,664	24,358	11,450
Interest charges	15,950	13,771	29,871	25,074
Income before income taxes	81,305	64,722	171,231	145,569
Income tax expense	12,108	8,574	24,642	19,783
Net income	69,197	56,148	146,589	125,786
Operating Segments | Purchased gas cost | Distribution segment
Purchased gas cost	809,023	993,854	1,690,938	1,490,653
Operating Segments | Purchased gas cost | Pipeline and storage segment
Purchased gas cost	621	1,683	(237)	(1,728)
Intersegment eliminations
Operating revenues	(143,661)	(124,474)	(286,707)	(247,028)
Purchased gas cost	(143,433)	(124,159)	(286,241)	(246,384)
Operation and maintenance expense	(228)	(315)	(466)	(644)
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
Intersegment eliminations | Distribution segment
Operating revenues	773	879	1,506	1,665
Intersegment eliminations | Pipeline and storage segment
Operating revenues	142,888	123,595	285,201	245,363
Intersegment eliminations | Purchased gas cost
Purchased gas cost	$ (143,433)	$ (124,159)	$ (286,241)	$ (246,384)