Derivative Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Short-term forward contracts, average maturities at inception	3 months
Foreign Currency Forward Contracts
Derivative [Line Items]
Forward foreign currency contracts fair value	$ 0	$ 0

Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

Name:	us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant