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Supplementary Information for Exploration and Production Activities - Capitalized Costs Relating to Exploration and Production Activities (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024
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Supplementary Information for Exploration and Production Activities Unaudited [Abstract] |  |  |
Proved Properties | [1] | $ 7,719,339 | $ 7,079,903
Unproved Properties |  | 112,432 | 200,986
Capitalized costs relating to exploration and production activities, gross |  | 7,831,771 | 7,280,889
Less — Accumulated Depreciation, Depletion and Amortization |  | 5,374,360 | 5,004,299
Capitalized costs relating to exploration and production activities, net |  | 2,457,411 | 2,276,590
Asset retirement costs |  | $ 233,900 | $ 175,200
[1] | Includes asset retirement costs of $233.9 million and $175.2 million at September 30, 2025 and 2024, respectively.

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- Definition Amount of accumulated depreciation, depletion, amortization, and valuation allowance for capitalized cost in oil- and gas-producing activities. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 55 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477916/932-235-55-3 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-15 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-15 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-13 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-12 + Details
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- Definition Amount, before accumulated depreciation, depletion, amortization, and valuation allowance, of capitalized cost for asset retirement in oil- and gas-producing activities. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-15 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-15 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 932 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477215/932-235-50-13 + Details
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