CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Operating revenues	$ 977,665	$ 1,094,645	$ 1,853,228	$ 1,972,427
Purchased gas cost	317,883	471,676	614,751	813,841
Operation and maintenance expense	147,824	149,427	300,069	288,027
Depreciation and amortization expense	105,916	96,772	210,978	192,837
Taxes, other than income	74,604	79,093	143,211	143,581
Operating income	331,438	297,677	584,219	534,141
Other non-operating income (expense)	(2,989)	4,232	1,898	(3,491)
Interest charges	22,171	26,949	49,400	54,798
Income before income taxes	306,278	274,960	536,717	475,852
Income tax expense	66,632	60,072	118,398	103,318
Net income	$ 239,646	$ 214,888	$ 418,319	$ 372,534
Basic net income per share (USD per share)	$ 1.95	$ 1.83	$ 3.43	$ 3.22
Diluted net income per share (USD per share)	1.95	1.82	3.42	3.21
Cash dividends per share (USD per share)	$ 0.575	$ 0.525	$ 1.15	$ 1.05
Basic weighted average shares outstanding (in shares)	122,916	117,581	122,015	115,690
Diluted weighted average shares outstanding (in shares)	122,997	117,756	122,179	115,794
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax of $(49) and $29	$ (163)	$ 97	$ (164)	$ 97
Cash flow hedges:
Amortization and unrealized loss on interest rate agreements, net of tax of $623 and $(7,405)	1,053	(2,792)	2,106	(25,050)
Total other comprehensive income (loss)	890	(2,695)	1,942	(24,953)
Total comprehensive income	240,536	212,193	420,261	347,581
Distribution segment
Operating revenues	932,296	1,057,192	1,760,136	1,895,373
Pipeline and storage segment
Operating revenues	45,369	37,453	93,092	77,054
Operating Segments | Distribution segment
Operating revenues	933,005	1,057,889	1,761,509	1,896,724
Purchased gas cost	418,935	570,348	816,493	1,008,080
Operation and maintenance expense	115,851	117,621	230,203	223,388
Depreciation and amortization expense	76,265	69,904	152,339	139,613
Taxes, other than income	68,413	71,053	128,656	127,243
Operating income	253,541	228,963	433,818	398,400
Other non-operating income (expense)	(5,191)	5,263	(3,237)	(1,214)
Interest charges	10,797	15,896	27,159	34,106
Income before income taxes	237,553	218,330	403,422	363,080
Income tax expense	50,489	46,137	86,601	76,502
Net income	187,064	172,193	316,821	286,578
Operating Segments | Pipeline and storage segment
Operating revenues	146,237	135,650	294,413	270,120
Purchased gas cost	202	(90)	301	(448)
Operation and maintenance expense	32,296	32,118	70,517	65,265
Depreciation and amortization expense	29,651	26,868	58,639	53,224
Taxes, other than income	6,191	8,040	14,555	16,338
Operating income	77,897	68,714	150,401	135,741
Other non-operating income (expense)	2,202	(1,031)	5,135	(2,277)
Interest charges	11,374	11,053	22,241	20,692
Income before income taxes	68,725	56,630	133,295	112,772
Income tax expense	16,143	13,935	31,797	26,816
Net income	52,582	42,695	101,498	85,956
Intersegment eliminations
Operating revenues	(101,577)	(98,894)	(202,694)	(194,417)
Purchased gas cost	(101,254)	(98,582)	(202,043)	(193,791)
Operation and maintenance expense	(323)	(312)	(651)	(626)
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 (expense)	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	709	697	1,373	1,351
Intersegment eliminations | Pipeline and storage segment
Operating revenues	100,868	98,197	201,321	193,066
Natural Gas, US Regulated
Purchased gas cost	317,883	471,676	614,751	813,841
Natural Gas, US Regulated | Operating Segments | Distribution segment
Purchased gas cost	418,935	570,348	816,493	1,008,080
Natural Gas, US Regulated | Operating Segments | Pipeline and storage segment
Purchased gas cost	202	(90)	301	(448)
Natural Gas, US Regulated | Intersegment eliminations
Purchased gas cost	$ (101,254)	$ (98,582)	$ (202,043)	$ (193,791)