Quarterly Financial Data (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Revenues	$ 287,989		$ 323,019		$ 491,095		$ 444,188	$ 293,341	$ 357,200	$ 552,544	$ 490,247		$ 1,546,291	$ 1,693,332	$ 1,592,668
Operating Income	(173,979)		80,397		(24,580)		148,020	83,940	112,827	153,359	161,683		29,858	511,809	519,723
Net Income Available for Common Stock	$ (145,545)	[1]	$ 41,250	[2]	$ (106,068)	[3]	$ 86,591	$ 47,282	$ 63,753	$ 90,595	$ 102,660	[4]	$ (123,772)	$ 304,290	$ 391,521
Earnings per Common Share, Basic	$ (1.60)		$ 0.47		$ (1.23)		$ 1.00	$ 0.55	$ 0.74	$ 1.05	$ 1.19		$ (1.41)	$ 3.53	$ 4.56
Earnings per Common Share, Diluted	$ (1.60)		$ 0.47		$ (1.23)		$ 1.00	$ 0.54	$ 0.73	$ 1.04	$ 1.18		$ (1.41)	$ 3.51	$ 4.53
Impairment of Oil and Gas Producing Properties	$ 253,400		$ 18,200		$ 177,800								$ 449,438	$ 0	$ 0
Impairment of Oil and Gas Producing Properties After Tax	183,700		$ 13,300		129,300
Valuation Allowance	$ 63,205				$ 56,800			$ 0					$ 63,205	$ 0
Increase (Reduction) to Income Tax Expense Due to Remeasurement of Deferred Income Tax Assets and Liabilites											$ (5,000)

[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.