Goodwill - Schedule of Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended
Mar. 31, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	$ 841,529
Accumulated impairment	(574,885)	$ (574,885)
Goodwill, net, beginning balance	266,644
Changes during the period	0
Goodwill, gross, ending balance	841,529
Goodwill, net, ending balance	266,644
Americas
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	773,384
Accumulated impairment	(569,201)	(569,201)
Goodwill, net, beginning balance	204,183
Changes during the period	0
Goodwill, gross, ending balance	773,384
Goodwill, net, ending balance	204,183
EMEA
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	51,190
Accumulated impairment	0	0
Goodwill, net, beginning balance	51,190
Changes during the period	0
Goodwill, gross, ending balance	51,190
Goodwill, net, ending balance	51,190
APAC
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	16,955
Accumulated impairment	(5,684)	$ (5,684)
Goodwill, net, beginning balance	11,271
Changes during the period	0
Goodwill, gross, ending balance	16,955
Goodwill, net, ending balance	$ 11,271

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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- Definition

Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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