Quarterly Financial Data (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended															12 Months Ended
	Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Operating Revenues	$ 292,472		$ 335,617		$ 449,132		$ 375,195		$ 301,062		$ 339,815		$ 596,127		$ 523,909	$ 1,452,416	$ 1,760,913	$ 2,113,081
Operating Income (Loss)	81,244		45,162		(237,000)		(305,924)		(326,731)		(489,214)		44,331		160,561	(416,518)	(611,053)	569,673
Net Income (Loss) Available for Common Stock	$ 37,553	[1]	$ 8,286	[2]	$ (147,688)	[3]	$ (189,109)	[4]	$ (187,703)	[5]	$ (293,134)	[6]	$ 16,669	[7]	$ 84,741	$ (290,958)	$ (379,427)	$ 299,413
Earnings (Loss) per Common Share, Basic	$ 0.44		$ 0.10		$ (1.74)		$ (2.23)		$ (2.22)		$ (3.47)		$ 0.20		$ 1.01	$ (3.43)	$ (4.50)	$ 3.57
Earnings (Loss) per Common Share, Diluted	$ 0.44		$ 0.10		$ (1.74)		$ (2.23)		$ (2.22)		$ (3.44)		$ 0.20		$ 1.00	$ (3.43)	$ (4.50)	$ 3.52
Impairment of Oil and Gas Producing Properties	$ 32,700		$ 82,700		$ 397,400		$ 435,500		$ 417,200		$ 588,700		$ 120,300			$ 948,307	$ 1,126,257	$ 0
Impairment of Oil and Gas Producing Properties After Tax	$ 19,000		$ 47,900		$ 230,500		$ 252,600		240,900		$ 339,800		$ 69,500
Reversal of Stock-Based Compensation Expense									8,000							$ 8,000
Reversal of Stock-based Compensation Expense, After Tax									$ 4,700

[1] Includes a non-cash $32.7 million impairment charge ($19.0 million after tax) associated with the Exploration and Production segment's oil and gas producing properties

[2] Includes a non-cash $82.7 million impairment charge ($47.9 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $397.4 million impairment charge ($230.5 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[4] Includes a non-cash $435.5 million impairment charge ($252.6 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[5] Includes a non-cash $417.2 million impairment charge ($240.9 million after tax) associated with the Exploration and Production segment's oil and gas producing properties and a $8.0 million reversal of stock-based compensation expense ($4.7 million after tax) related to performance based restricted stock units.

[6] Includes a non-cash $588.7 million impairment charge ($339.8 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[7] Includes a non-cash $120.3 million impairment charge ($69.5 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.