Significant Accounting Policies and Practices - Summary Of Transactions Related Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Total transaction-related charges	$ 23.1	$ 21.8	$ 30.2
Coevorden operations divestiture
Business Acquisition [Line Items]
Total transaction-related charges	5.5	0.0	0.0
GBL post divestiture separation
Business Acquisition [Line Items]
Total transaction-related charges	10.2	9.5	0.0
HPC divestiture
Business Acquisition [Line Items]
Total transaction-related charges	3.9	7.3	14.9
PetMatrix integration
Business Acquisition [Line Items]
Total transaction-related charges	0.0	0.0	4.9
Omega Sea acquisition
Business Acquisition [Line Items]
Total transaction-related charges	1.6	0.0	0.0
Other integration
Business Acquisition [Line Items]
Total transaction-related charges	$ 1.9	$ 5.0	$ 10.4