Asset Acquisition and Divestitures (Summary of Asset Acquisition) (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Asset Acquisition and Divestitures [Line Items]
Property, Plant and Equipment		$ 829,388	$ 769,911	$ 1,228,617
Shell Acquisition [Member]
Asset Acquisition and Divestitures [Line Items]
Purchase Price				503,908
Transaction Costs				2,350
Total Consideration				506,258
Property, Plant and Equipment				505,017
Inventory				1,241
Total Accounting				506,258
Exploration And Production [Member]
Asset Acquisition and Divestitures [Line Items]
Property, Plant and Equipment		565,791	381,408	670,455
Exploration And Production [Member] | Shell Acquisition [Member]
Asset Acquisition and Divestitures [Line Items]
Property, Plant and Equipment	[1],[2]			281,648
Inventory				1,132
Total Accounting				282,780
Proved Developed Producing Properties				241,134
Property Plant and Equipment Capitalized in the Full Cost Pool				277,832
Gathering [Member]
Asset Acquisition and Divestitures [Line Items]
Property, Plant and Equipment		$ 55,546	$ 34,669	297,806
Gathering [Member] | Shell Acquisition [Member]
Asset Acquisition and Divestitures [Line Items]
Property, Plant and Equipment	[2]			223,369
Inventory				109
Total Accounting				$ 223,478

[1] Includes $241,134 in Proved Developed Producing Properties and $277,832 capitalized in the full cost pool.

[2] The Company utilized an income approach and market based approach to determine the fair value of the acquired property, plant and equipment in the Exploration and Production reporting segment. The Company utilized a cost approach and an income approach to determine the fair value of the acquired property, plant and equipment in the Gathering reporting segment.