Summary of Significant Accounting Policies - Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales	$ 1,247.1	$ 988.3	$ 854.4
Cost of goods sold	860.9	650.3	542.6
Gross profit	386.2	338.0	311.8
Selling, general and administrative expenses	167.1	151.8	127.1
Amortization of intangible assets	51.2	22.2	22.2
Operating profit	168.0	164.0	162.5
Trade promotion allowance, current	$ 19.4	$ 14.7
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales			863.2
Cost of goods sold			542.6
Gross profit			320.6
Selling, general and administrative expenses			135.9
Amortization of intangible assets			22.2
Operating profit			162.5
Difference between revenue guidance in effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales			8.8
Cost of goods sold			0.0
Gross profit			8.8
Selling, general and administrative expenses			8.8
Amortization of intangible assets			0.0
Operating profit			$ 0.0