Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018
Derivative Instruments and Hedging Activities
Asset derivatives	$ 5,618	$ 2,117
Liability derivatives	3,367	1,732
Foreign currency forwards \| Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	5,036	1,803
Foreign currency forwards \| Other noncurrent assets
Derivative Instruments and Hedging Activities
Asset derivatives	582	314
Foreign currency forwards \| Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	$ 3,367	1,657
Foreign currency forwards \| Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives		$ 75

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: 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

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant