Derivative Financial Instruments - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Net losses on foreign currency exposures	$ 1.7	$ 3.2	$ 7.0
Net realized and unrealized gain or (loss) (excluding the underlying foreign currency exposure being hedged)	$ 7.0	$ (8.4)	$ (7.5)
Forward Contracts \| Designated as Hedging Instrument \| Net Investment Hedging
Derivative [Line Items]
Derivative, remaining maturity	3 months

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Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Amount before tax of foreign currency transaction realized and unrealized loss recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 50
-Paragraph 1
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-Name Accounting Standards Codification
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Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of foreign currency derivatives not designated as hedging instruments.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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