Business Segment Information (Narrative) (Details) $ in Thousands	3 Months Ended													12 Months Ended
	Sep. 30, 2015 USD ($)	[1]	Jun. 30, 2015 USD ($)	[2]	Mar. 31, 2015 USD ($)	[3]	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	[2]	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	[4]	Dec. 31, 2013 USD ($)	Sep. 30, 2015 USD ($) segment	Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment														5
Segment Profit: Net Income (Loss)	$ (187,703)		$ (293,134)		$ 16,669		$ 84,741	$ 57,431		$ 64,520	$ 95,210		$ 82,252	$ (379,427)	$ 299,413	$ 260,001
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)														7,766	$ 6,631	$ 4,589
Energy Marketing [Member] | Margin [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)														600
Unbilled Revenues [Member] | Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers														$ 8,500

[1] 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 ($5.2 million after tax) related to performance based restricted stock units.

[2] 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.

[3] 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.

[4] Includes $3.6 million of income associated with a death benefit gain on life insurance proceeds recorded in the Corporate category.