Financial Instruments and Hedging Activities (Additional Information) (Detail) - Derivatives Not Designated as Hedges - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2019	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Notional Amount	$ 43.6	$ 117.1
Maximum
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Term of foreign currency forward contracts	90 days

Average period remaining before foreign currency exchange rate derivatives mature or expire, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_AverageRemainingMaturityOfForeignCurrencyDerivatives1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration