CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Operating revenues
Total operating revenues	$ 1,094,645	$ 1,219,409	$ 1,972,427	$ 2,108,601
Operation and maintenance expense	149,427	159,159	288,027	288,204
Depreciation and amortization expense	96,772	89,381	192,837	177,755
Taxes, other than income	79,093	73,007	143,581	135,780
Operating income	297,677	270,902	534,141	512,985
Other non-operating income (expense)	4,232	(2,167)	(3,491)	(4,724)
Interest charges	26,949	27,304	54,798	58,813
Income before income taxes	274,960	241,431	475,852	449,448
Income tax expense	60,072	62,439	103,318	(43,676)
Net income	$ 214,888	$ 178,992	$ 372,534	$ 493,124
Basic net income per share	$ 1.83	$ 1.60	$ 3.22	$ 4.47
Diluted net income per share	1.82	1.60	3.21	4.47
Cash dividends per share	$ 0.525	$ 0.485	$ 1.050	$ 0.970
Basic weighted average shares outstanding	117,581	111,706	115,690	110,135
Diluted weighted average shares outstanding	117,756	111,706	115,794	110,135
Other comprehensive income (loss), net of tax
Net unrealized holding gains (losses) on available-for-sale securities, net of tax	$ 97	$ (939)	$ 97	$ (1,046)
Cash flow hedges:
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(2,792)	22,244	(25,050)	21,289
Total other comprehensive income (loss)	(2,695)	21,305	(24,953)	20,243
Total comprehensive income	212,193	200,297	347,581	513,367
Operating Segments | Distribution segment
Operating revenues
Total operating revenues	1,057,889	1,199,291	1,896,724	2,060,083
Operation and maintenance expense	117,621	130,077	223,388	233,292
Depreciation and amortization expense	69,904	65,649	139,613	131,083
Taxes, other than income	71,053	64,692	127,243	119,799
Operating income	228,963	211,820	398,400	385,098
Other non-operating income (expense)	5,263	(1,521)	(1,214)	(3,443)
Interest charges	15,896	16,898	34,106	38,266
Income before income taxes	218,330	193,401	363,080	343,389
Income tax expense	46,137	48,158	76,502	(50,953)
Net income	172,193	145,243	286,578	394,342
Operating Segments | Pipeline and storage segment
Operating revenues
Total operating revenues	135,650	120,955	270,120	247,418
Operation and maintenance expense	32,118	29,393	65,265	55,533
Depreciation and amortization expense	26,868	23,732	53,224	46,672
Taxes, other than income	8,040	8,315	16,338	15,981
Operating income	68,714	59,082	135,741	127,887
Other non-operating income (expense)	(1,031)	(646)	(2,277)	(1,281)
Interest charges	11,053	10,406	20,692	20,547
Income before income taxes	56,630	48,030	112,772	106,059
Income tax expense	13,935	14,281	26,816	7,277
Net income	42,695	33,749	85,956	98,782
Intersegment eliminations
Operating revenues
Total operating revenues	(98,894)	(100,837)	(194,417)	(198,900)
Operation and maintenance expense	(312)	(311)	(626)	(621)
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
Natural Gas, US Regulated
Operating revenues
Cost of Revenue	471,676	626,960	813,841	993,877
Natural Gas, US Regulated | Operating Segments | Distribution segment
Operating revenues
Cost of Revenue	570,348	727,053	1,008,080	1,190,811
Natural Gas, US Regulated | Operating Segments | Pipeline and storage segment
Operating revenues
Cost of Revenue	(90)	433	(448)	1,345
Natural Gas, US Regulated | Intersegment eliminations
Operating revenues
Cost of Revenue	$ (98,582)	$ (100,526)	$ (193,791)	$ (198,279)