Derivative Instruments - Notional Amounts (Details)	6 Months Ended
	Mar. 31, 2021 $ / bbl bbl
Crude Oil Swap, Q2 2021
Derivative [Line Items]
Notional Volume | bbl	527,768,000
Weighted average price (in usd per bbl)	51.38
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	960,000,000
Weighted average price (in usd per bbl)	51.05
Crude Oil Swap, 2023
Derivative [Line Items]
Notional Volume | bbl	30,000,000
Weighted average price (in usd per bbl)	52.11
Natural Gas Swaps, Q2 2021
Derivative [Line Items]
Notional Volume | bbl	450,000,000
Weighted average price (in usd per bbl)	2.97
Natural Gas Swaps, Q3 2021
Derivative [Line Items]
Notional Volume | bbl	450,000,000
Weighted average price (in usd per bbl)	2.97
Natural Gas Swaps, Q4 2021
Derivative [Line Items]
Notional Volume | bbl	450,000,000
Weighted average price (in usd per bbl)	2.97
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, Q2 2021
Derivative [Line Items]
Notional Volume | bbl	435,000,000
Weighted average price (in usd per bbl)	0.40
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	240,000,000
Weighted average price (in usd per bbl)	0.70