Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2021
Income Tax Disclosure [Line Items]
Income tax expense (benefits), tax credit, discrete items		$ 8.0	$ 1.9	$ (21.7)
Income tax expense (benefit), discrete items, percentage of pre-tax income		1.80%	0.30%	(3.60%)
Effective income tax rate reconciliation, at federal statutory income tax rate, percent	35.00%	21.00%	21.00%	24.50%
Tax cuts and jobs act, change in tax rate, income tax expense (benefit)				$ (30.2)
Tax cuts and jobs act, deferred tax asset		$ 44.8	$ 44.8
Tax cuts and jobs act, income tax payable		61.0	61.0
Deferred tax assets, valuation allowance		17.4	1.1
Undistributed earnings in non-U.S. subsidiaries		392.5
Foreign and domestic income taxes and withholding taxes		24.3
Potential tax liability		18.4
Net unrecognized tax benefits, excluding interest and penalties that would affect the company's net income if recognized		17.2
Interest and penalties		1.3	0.1	$ (3.7)
Accruals for payment of interest and penalties		5.7	$ 4.4
Scenario Forecast
Income Tax Disclosure [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, amount of unrecorded benefit					$ 7.3
Foreign Tax Authority
Income Tax Disclosure [Line Items]
Valuation allowance on foreign net deferred tax assets		11.5
Operating loss carryforwards		$ 42.0
Tax credit carryforwards, foreign expiration period, minimum		7 years
Deferred tax assets, operating loss carryforwards		$ 10.7
Deferred tax assets, valuation allowance		17.4
State and Local Jurisdiction
Income Tax Disclosure [Line Items]
Operating loss carryforwards		$ 167.7
Tax credit carryforwards, state expiration period, minimum		5 years
Tax credit carryforward, amount		$ 25.8
Tax credit carryforwards, expiration year start		2026
Tax credit carryforwards, expiration year end		2035
Deferred tax assets, operating loss carryforwards		$ 6.6
Deferred tax assets, tax credit carryforwards		$ 17.2