Derivative Financial Instruments - Schedule of Derivative Instruments and Hedging Activities Disclosures (Details) - Foreign Exchange Forward - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Not Designated as Hedging Instrument \| Other income (expense), net
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized gain (loss), excluding the underlying foreign currency exposure being hedged	$ 3,518	$ (11,314)	$ (9,720)
Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Gain (loss) recognized in OCI—effective portion	0	187	1,652
Gain (loss) reclassified from OCI into income—effective portion	0	627	(552)
Gain (loss) recognized—ineffective portion	0	0	21
Designated as Hedging Instrument \| Net Investment Hedging
Derivative Instruments Gain Loss [Line Items]
Gain (loss) recognized in OCI—effective portion	(5,483)	(2,925)	0
Gain (loss) reclassified from OCI—effective portion	109	(7,630)	0
Designated as Hedging Instrument \| Other income (expense), net \| Net Investment Hedging
Derivative Instruments Gain Loss [Line Items]
Gain (loss) recognized—portion excluded from effectiveness testing	$ 3,506	$ 4,598	$ 0

Amount of gain (loss) from excluded component of derivative hedge, recognized in earnings. Excludes recognition under systematic and rational method.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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The amount of net gains or losses on foreign currency cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

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The net gain (loss) during the reporting period due to ineffectiveness in foreign currency cash flow hedges. Recognized in earnings.

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Amount, before tax, of reclassification from accumulated other comprehensive income (AOCI) for gain (loss) from derivative designated and qualifying as net investment hedge.

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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