Summary of Significant Accounting Policies - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Accrued capital expenditures	$ 9,271	$ 2,964
Accrued lease operating expenses	2,815	1,617
Accrued ad valorem tax	352	680
Accrued general and administrative costs	2,619	2,125
Accrued interest expense	24	63
Accrued dividends on preferred units	0	903
Accrued dividends on common units and shares	38	95
Other accrued expenditures	2,029	299
Total accrued liabilities	$ 17,148	$ 8,746