Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Apr. 22, 2020	Oct. 01, 2019	Apr. 01, 2019	Feb. 28, 2018
Finite-Lived Intangible Assets [Line Items]
Maximum amount authorized to sell	$ 500,000,000.0
Receivables sold under program	439,500,000	$ 300,200,000
Outstanding sold receivables	132,900,000	87,800,000
Receivables collected but not yet due	500,000	12,400,000
Fees associated with factoring	4,700,000	4,900,000
Amortization expense	8,100,000	9,100,000	$ 7,400,000
Depreciation excluding accelerated	63,200,000	43,500,000	26,200,000
Accelerated depreciation	15,900,000	3,000,000.0
Advertising costs	115,100,000	96,700,000	$ 80,100,000
Operating lease assets	121,900,000	0
Operating lease liability	126,700,000
Cash and cash equivalents	459,800,000	258,500,000
Interest Rate Swap
Finite-Lived Intangible Assets [Line Items]
Variable rate debt hedged	200,000,000.0	$ 200,000,000.0
Interest rate on derivative instrument							2.47%
Notional value	$ 100,000,000.0					$ 50,000,000.0	$ 400,000,000.0
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period, years	3 years
Minimum | Computer Software, Intangible Asset
Finite-Lived Intangible Assets [Line Items]
Amortization period, years	3 years
Minimum | Pro Forma | Accounting Standards Update 2016-02
Finite-Lived Intangible Assets [Line Items]
Operating lease liability					$ 40,000,000
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period, years	15 years
Maximum | Computer Software, Intangible Asset
Finite-Lived Intangible Assets [Line Items]
Amortization period, years	7 years
Maximum | Pro Forma | Accounting Standards Update 2016-02
Finite-Lived Intangible Assets [Line Items]
Operating lease liability					$ 45,000,000
Machinery and Equipment | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life, years	2 years
Machinery and Equipment | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life, years	25 years
Building and Building Improvements | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life, years	3 years
Building and Building Improvements | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life, years	30 years
Restricted Stock Equivalents | Minimum
Finite-Lived Intangible Assets [Line Items]
Vesting period, in years	2 years
Restricted Stock Equivalents | Maximum
Finite-Lived Intangible Assets [Line Items]
Vesting period, in years	4 years
Senior Notes, 4.375%, Due 2029 | Senior Notes
Finite-Lived Intangible Assets [Line Items]
Face amount of debt	$ 800,000,000.0
Stated interest rate of debt	4.375%
6.375% Senior Notes due 2026 | Senior Notes
Finite-Lived Intangible Assets [Line Items]
Face amount of debt				$ 250,000,000.0
Stated interest rate of debt	6.375%			6.375%
International | Cash
Finite-Lived Intangible Assets [Line Items]
Percentage of cash outside of the U.S.	61.80%	75.80%