Benefit Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Contribution Plan Disclosure [Line Items]
Employee matching contribution, percent	60.00%
Employee contributions match	$ 300,000	$ 300,000	$ 300,000
Pension Plan | NIGPP
Defined Contribution Plan Disclosure [Line Items]
Multiemployer plan, agreement renewal period			3 years
Multiemployer plan, agreement expiration date			Sep. 30, 2022
Multiemployer plan, contribution rate per hour, per employee	2.55
Multiemployer plan, contribution amount	$ 39,000	$ 44,000	$ 53,000
Maximum
Defined Contribution Plan Disclosure [Line Items]
Employee participants eligible compensation each payroll period, percent	3.60%