Employee Benefit Plans - Additional Information (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Defined Contribution Plan Service Period	90 days
Description of Defined Contribution Pension and Other Postretirement Plans	The Company currently matches the first 50% of participant contributions limited to 6% of a participant’s gross compensation (maximum Company match is 3%).
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	100.00%
Defined Contribution Plan Minimum Annual Contributions Per Employee Percent	1.00%
Defined First 50% of Participant Contribution Plan	50.00%
Defined Contribution Plan, Cost Recognized	$ 12.1	$ 11.7	$ 11.8
Pension Contributions	1.7	1.0	0.2
Multi-employer defined benefit plans aggregated expense	$ 2.5	$ 2.6	$ 1.8
Minimum [Member]
Defined Contribution Plan Qualifying Age	21
Maximum [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	3.00%