CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating revenues	$ 914,480	$ 875,563
Purchased gas cost	288,260	296,868
Operation and maintenance expense	138,643	152,245
Depreciation and amortization expense	115,285	105,062
Taxes, other than income	73,452	68,607
Operating income	298,840	252,781
Other non-operating income	6,072	4,887
Interest charges	22,010	27,229
Income before income taxes	282,902	230,439
Income tax expense	65,224	51,766
Net income	$ 217,678	$ 178,673
Basic net income per share (USD per share)	$ 1.71	$ 1.47
Diluted net income per share (USD per share)	1.71	1.47
Cash dividends per share (USD per share)	$ 0.625	$ 0.575
Basic weighted average shares outstanding (in shares)	127,034	121,113
Diluted weighted average shares outstanding (in shares)	127,034	121,359
Other comprehensive income (loss), net of tax
Net unrealized holding gains on available-for-sale securities, net of tax	$ (63)	$ (1)
Cash flow hedges:
Amortization and unrealized gain (loss) on interest rate agreements, net of tax	60,184	1,053
Total other comprehensive income (loss)	60,121	1,052
Total comprehensive income	277,799	179,725
Distribution segment
Operating revenues	875,887	827,840
Pipeline and storage segment
Operating revenues	38,593	47,723
Operating Segments | Distribution segment
Operating revenues	876,650	828,504
Purchased gas cost	411,072	397,558
Operation and maintenance expense	108,802	114,352
Depreciation and amortization expense	82,870	76,074
Taxes, other than income	64,352	60,243
Operating income	209,554	180,277
Other non-operating income	835	1,954
Interest charges	10,712	16,362
Income before income taxes	199,677	165,869
Income tax expense	45,985	36,112
Net income	153,692	129,757
Operating Segments | Pipeline and storage segment
Operating revenues	159,713	148,176
Purchased gas cost	(1,244)	99
Operation and maintenance expense	30,156	38,221
Depreciation and amortization expense	32,415	28,988
Taxes, other than income	9,100	8,364
Operating income	89,286	72,504
Other non-operating income	5,237	2,933
Interest charges	11,298	10,867
Income before income taxes	83,225	64,570
Income tax expense	19,239	15,654
Net income	63,986	48,916
Eliminations
Operating revenues	(121,883)	(101,117)
Purchased gas cost	(121,568)	(100,789)
Operation and maintenance expense	(315)	(328)
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
Eliminations | Distribution segment
Operating revenues	763	664
Eliminations | Pipeline and storage segment
Operating revenues	121,120	100,453
Purchased gas cost
Purchased gas cost	288,260	296,868
Purchased gas cost | Operating Segments | Distribution segment
Purchased gas cost	411,072	397,558
Purchased gas cost | Operating Segments | Pipeline and storage segment
Purchased gas cost	(1,244)	99
Purchased gas cost | Eliminations
Purchased gas cost	$ (121,568)	$ (100,789)