Derivative Financial Instruments - Gains (Losses) on Derivative Financial Instruments Recorded in Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Foreign currency forward contracts
Derivative [Line Items]
Gains (losses) on foreign currency forward contracts	$ (404)	$ 194

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

Name:	us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration