Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
INCOME
Operating Revenues	$ 552,544	$ 540,905	$ 1,042,791	$ 960,561
Operating Expenses:
Property, Franchise and Other Taxes	22,535	22,802	46,540	43,650
Depreciation, Depletion and Amortization	65,664	61,155	129,918	116,985
Total Operating Expenses	399,185	369,316	727,748	639,502
Operating Income	153,359	171,589	315,043	321,059
Other Income (Expense):
Other Income (Deductions)	(5,919)	(13,092)	(15,521)	(16,594)
Interest Expense on Long-Term Debt	(25,273)	(27,148)	(50,713)	(55,235)
Other Interest Expense	(1,787)	(1,233)	(2,860)	(1,736)
Income Before Income Taxes	120,380	130,116	245,949	247,494
Income Tax Expense (Benefit)	29,785	38,269	52,693	(43,007)
Net Income Available for Common Stock	90,595	91,847	193,256	290,501
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,172,334	1,014,733	1,098,900	851,669
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,262,929	1,106,580	1,292,156	1,142,170
Dividends on Common Stock	(36,678)	(35,641)	(73,342)	(71,231)
Balance at March 31	$ 1,236,657	$ 1,070,939	$ 1,236,657	$ 1,070,939
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in dollars per share)	$ 1.05	$ 1.07	$ 2.24	$ 3.39
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in dollars per share)	$ 1.04	$ 1.06	$ 2.23	$ 3.37
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	86,290,047	85,809,233	86,159,932	85,718,779
Used in Diluted Calculation (shares)	86,767,673	86,323,636	86,738,809	86,318,892
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.425	$ 0.415	$ 0.850	$ 0.830
Purchased Gas [Member]
Operating Expenses:
Purchased Gas	$ 195,037	$ 176,608	$ 333,697	$ 270,642
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	357,654	339,422	629,747	565,147
Operating Expenses:
Operation and Maintenance	48,559	46,708	92,475	90,789
Exploration and Production and Other [Member]
INCOME
Operating Revenues	146,467	147,868	310,403	288,318
Operating Expenses:
Operation and Maintenance	40,141	39,127	72,936	74,209
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	48,423	53,615	102,641	107,096
Operating Expenses:
Operation and Maintenance	27,249	22,916	52,182	43,227
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	0	0	7,437	0
Guidance for Reclassification of Stranded Tax Effects [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	$ 10,406	$ 0	$ 10,406	$ 0