Capitalization And Short-Term Borrowings (Summary Of Changes In Common Stock Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended												12 Months Ended
		Sep. 30, 2020		Jun. 30, 2020	[2]	Mar. 31, 2020	[3]	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2018
Schedule of Capitalization [Line Items]
Beginning balance (shares)								86,315,287						86,315,287
Beginning balance								$ 832,264						$ 832,264
Balance at Beginning of Year								1,272,601				$ 1,098,900		1,272,601		$ 1,098,900	$ 851,669
Beginning balance								(52,155)				(67,750)		(52,155)		(67,750)
Net Income (Loss) Available for Common Stock		$ (145,545)	[1]	$ 41,250		$ (106,068)		$ 86,591	$ 47,282	$ 63,753	$ 90,595	$ 102,660	[4]	(123,772)		304,290	391,521
Dividends Declared on Common Stock														(156,249)		(148,432)	(144,290)
Other Comprehensive Income (Loss), Net of Tax														(62,602)		15,595	(37,627)
Share-Based Payment Expense														$ 13,100		$ 19,500	14,200
Ending balance (Shares)		90,954,696							86,315,287					90,954,696		86,315,287
Ending balance		$ 1,004,158							$ 832,264					$ 1,004,158		$ 832,264
Balance at End of Year		991,630							1,272,601					991,630		1,272,601	1,098,900
Ending balance		(114,757)							$ (52,155)					$ (114,757)		$ (52,155)	$ (67,750)
Dividend per share														$ 1.76		$ 1.72	$ 1.68
Accumulated earnings free from limitations		$ 848,400												$ 848,400
Common Stock [Member]
Schedule of Capitalization [Line Items]
Beginning balance (shares)								86,315,000				85,957,000		86,315,000		85,957,000	85,543,000
Beginning balance (value)								$ 86,315				$ 85,957		$ 86,315		$ 85,957	$ 85,543
Common Stock Issued from Sale of Common Stock (Shares)														4,370,000
Common Stock Issued from Sale of Common Stock (Value)														$ 4,370
Common Stock Issued Under Stock and Benefit Plans (Shares)														270,000		358,000	414,000
Common Stock Issued Under Stock and Benefit Plans (Value)														$ 270		$ 358	$ 414
Ending balance (Shares)		90,955,000							86,315,000					90,955,000		86,315,000	85,957,000
Ending balance (Value)		$ 90,955							$ 86,315					$ 90,955		$ 86,315	$ 85,957
Paid In Capital [Member]
Schedule of Capitalization [Line Items]
Beginning balance								832,264				820,223		832,264		820,223	796,646
Share-Based Payment Expense	[5]													13,180		19,613	14,235
Common Stock Issued from Sale of Common Stock (Value)														161,399
Common Stock Issued Under Stock and Benefit Plans (Value)																	9,342
Stock Repurchased under Stock and Benefit Plans														(2,685)		(7,572)
Ending balance		1,004,158							832,264					1,004,158		832,264	820,223
Earnings Reinvested In The Business [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year								1,272,601				1,098,900		1,272,601		1,098,900	851,669
Net Income (Loss) Available for Common Stock														(123,772)		304,290	391,521
Dividends Declared on Common Stock														(156,249)		(148,432)	(144,290)
Balance at End of Year		991,630	[6]						1,272,601					991,630	[6]	1,272,601	1,098,900
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization [Line Items]
Beginning balance								(52,155)				(67,750)		(52,155)		(67,750)	(30,123)
Other Comprehensive Income (Loss), Net of Tax														(62,602)		15,595	(37,627)
Ending balance		$ (114,757)							(52,155)					(114,757)		(52,155)	(67,750)
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year								0				7,437		0		7,437	0
Balance at End of Year									0							0	7,437
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Earnings Reinvested In The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year												7,437				7,437
Balance at End of Year																	7,437
Guidance for Reclassification of Stranded Tax Effects [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year								0				10,406		0		10,406	0
Balance at End of Year									0							0	10,406
Guidance for Reclassification of Stranded Tax Effects [Member] | Earnings Reinvested In The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year												10,406				10,406
Balance at End of Year																	10,406
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year								(950)				$ 0		(950)		0	0
Balance at End of Year									(950)							(950)	$ 0
Guidance for Hedging [Member] | Earnings Reinvested In The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year								$ (950)						$ (950)
Balance at End of Year									$ (950)							$ (950)

[1] Includes a non-cash $253.4 million impairment charge ($183.7 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[2] Includes a non-cash $18.2 million impairment charge ($13.3 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $177.8 million impairment charge ($129.3 million after tax) associated with the Exploration and Production segment's oil and gas producing properties and a $56.8 million valuation allowance recorded against certain deferred tax assets.

[4] Includes a $5.0 million reduction to income tax expense associated with the remeasurement of accumulated deferred income taxes in accordance with the 2017 Tax Reform Act.

[5] Paid in Capital includes compensation costs associated with performance shares and/or restricted stock awards. The expense is included within Net Income Available for Common Stock, net of tax benefits.

[6] The availability of consolidated earnings reinvested in the business for dividends payable in cash is limited under terms of the indentures covering long-term debt. At September 30, 2020, $848.4 million of accumulated earnings was free of such limitations.