Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025		Sep. 30, 2024		Sep. 30, 2023
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Impairment of Assets	$ 141,802	[1]	$ 519,129	[1]	$ 0
Present Value of Contingent Consideration | California Asset Sale
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Value of contingent consideration from asset sale	0
Northern Access Project
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Impairment of Assets			46,100
Level 3 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Impairment of Assets	33,453		55,437		0
December 31, 2024 | Level 3 | Fair Value, Nonrecurring | Integrated Upstream and Gathering
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Impairment of Assets	33,453		0		0
September 30, 2024 | Level 3 | Fair Value, Nonrecurring | Integrated Upstream and Gathering
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Impairment of Assets	$ 0		$ 9,362		$ 0

[1] The Company considers this line to be a significant expense.