Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
INCOME
Operating Revenues	$ 323,019	$ 357,200	$ 1,258,301	$ 1,399,991
Operating Expenses:
Purchased Gas	29,121	47,839	239,663	381,537
Property, Franchise and Other Taxes	21,381	21,506	67,268	68,046
Depreciation, Depletion and Amortization	73,232	71,072	226,062	200,990
Impairment of Oil and Gas Producing Properties	18,236	0	195,997	0
Total Operating Expenses	242,622	244,373	1,054,465	972,122
Operating Income	80,397	112,827	203,836	427,869
Other Income (Expense):
Other Income (Deductions)	2,547	(1,456)	(17,971)	(16,977)
Interest Expense on Long-Term Debt	(27,140)	(25,303)	(77,853)	(76,016)
Other Interest Expense	(1,420)	(1,202)	(4,863)	(4,061)
Income Before Income Taxes	54,384	84,866	103,149	330,815
Income Tax Expense	13,134	21,113	81,376	73,806
Net Income Available for Common Stock	41,250	63,753	21,773	257,009
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,176,870	1,236,657	1,272,601	1,098,900
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,218,120	1,300,410	1,294,374	1,355,909
Dividends on Common Stock	(40,470)	(37,543)	(115,774)	(110,885)
Balance at June 30	$ 1,177,650	$ 1,262,867	$ 1,177,650	$ 1,262,867
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in dollars per share)	$ 0.47	$ 0.74	$ 0.25	$ 2.98
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in dollars per share)	$ 0.47	$ 0.73	$ 0.25	$ 2.96
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	87,966,289	86,306,434	86,966,448	86,208,766
Used in Diluted Calculation (shares)	88,323,699	86,839,841	87,346,362	86,765,781
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.445	$ 0.435	$ 1.315	$ 1.285
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 139,661	$ 151,312	$ 650,320	$ 781,059
Operating Expenses:
Operation and Maintenance	43,950	39,607	138,931	132,082
Exploration and Production and Other [Member]
INCOME
Operating Revenues	132,338	159,864	456,073	470,267
Operating Expenses:
Operation and Maintenance	32,404	35,674	109,056	108,610
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	51,020	46,024	151,908	148,665
Operating Expenses:
Operation and Maintenance	24,298	28,675	77,488	80,857
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	0	0	(950)	0
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	0	0	0	7,437
Guidance for Reclassification of Stranded Tax Effects [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	$ 0	$ 0	$ 0	$ 10,406