Benefit Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Contribution Plan Disclosure [Line Items]
Employee matching contribution, percent	60.00%
Employee contributions match	$ 300,000	$ 300,000	$ 400,000
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	2.48
Multiemployer plan, contribution amount	$ 44,000	$ 53,000	$ 64,000
Maximum
Defined Contribution Plan Disclosure [Line Items]
Employee participants eligible compensation each payroll period, percent	3.60%