Asset Acquisitions and Divestitures (Narrative) (Details)	3 Months Ended		9 Months Ended
	Jun. 30, 2023 USD ($) a	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) a	Jun. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)
Asset Acquisitions and Divestitures [Line Items]
Net Proceeds from Sale of Oil and Gas Producing Properties			$ 0	$ 254,439,000
Gain on Sale of Assets	$ 0	$ 12,736,000	$ 0	12,736,000
SWN Upstream Asset Acquisition [Member]
Asset Acquisitions and Divestitures [Line Items]
Net Acres Acquired in Appalachia | a	34,000		34,000
Total Consideration for Asset Acquisition of Upstream Assets			$ 124,758,000
California Asset Sale [Member]
Asset Acquisitions and Divestitures [Line Items]
Consideration for Asset Sale		253,500,000		253,500,000
Net Proceeds from Sale of Oil and Gas Producing Properties				240,900,000
Maximum Annual Contingent Payments		10,000,000		10,000,000
Amount of Each Incremental Contingent Payment		1,000,000		1,000,000
Incremental Dollar Per Barrel That ICE Brent Average Exceeds Price		1		1
Gain on Sale of Assets				12,700,000
Asset Retirement Obligation Reduction				50,100,000
California Asset Sale [Member] | Minimum [Member]
Asset Acquisitions and Divestitures [Line Items]
ICE Brent Average per Barrel		95		95
California Asset Sale [Member] | Maximum [Member]
Asset Acquisitions and Divestitures [Line Items]
ICE Brent Average per Barrel		105		105
California Asset Sale [Member] | Present Value of Contingent Consideration [Member]
Asset Acquisitions and Divestitures [Line Items]
Value of Contingent Consideration from Asset Sale	$ 4,500,000	12,600,000	$ 4,500,000	12,600,000	$ 8,200,000
Full Cost Method of Accounting Assets [Member] | California Asset Sale [Member]
Asset Acquisitions and Divestitures [Line Items]
Property, Plant and Equipment Disposal		220,700,000		220,700,000
Assets Not Subject to Full Cost Method of Accounting [Member] | California Asset Sale [Member]
Asset Acquisitions and Divestitures [Line Items]
Property, Plant and Equipment Disposal		$ 32,800,000		$ 32,800,000