Derivative Instruments - Notional Amounts, Crude Oil and Natural Gas (Details)	9 Months Ended
	Jun. 30, 2021 $ / bbl bbl
Crude Oil Swap, Q3 2021
Derivative [Line Items]
Notional Volume | bbl	564,278,000
Weighted average price (in USD per BBL)	51.57
Crude Oil Swap, Q4 2021
Derivative [Line Items]
Notional Volume | bbl	558,116,000
Weighted average price (in USD per BBL)	51.65
Crude Oil Swap, 2022
Derivative [Line Items]
Notional Volume | bbl	1,320,000,000
Weighted average price (in USD per BBL)	53.59
Crude Oil Swap, 2023
Derivative [Line Items]
Notional Volume | bbl	360,000,000
Weighted average price (in USD per BBL)	59.01
Natural Gas Swaps, Q3 2021
Derivative [Line Items]
Notional Volume | bbl	555,000,000
Weighted average price (in USD per BBL)	3.03
Natural Gas Swaps, Q4 2021
Derivative [Line Items]
Notional Volume | bbl	555,000,000
Weighted average price (in USD per BBL)	3.03
Crude Oil Collars, 2022
Derivative [Line Items]
Notional Volume | bbl	360,000,000
Crude Oil Collars, 2022 | Short
Derivative [Line Items]
Weighted average price (in USD per BBL)	35.00
Crude Oil Collars, 2022 | Long
Derivative [Line Items]
Weighted average price (in USD per BBL)	42.63
Crude Oil Basis, Q3 2021
Derivative [Line Items]
Notional Volume | bbl	435,000,000
Weighted average price (in USD per BBL)	0.40
Crude Oil Basis, Q4 2021
Derivative [Line Items]
Notional Volume | bbl	435,000,000
Weighted average price (in USD per BBL)	0.40
Crude Oil Basis, 2022
Derivative [Line Items]
Notional Volume | bbl	720,000,000
Weighted average price (in USD per BBL)	0.40