Goodwill and Intangible Assets (Goodwill and Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	6 Months Ended
Mar. 31, 2018	Sep. 30, 2017
Goodwill (not amortized), Net Book Value	$ 1,191,603	$ 1,182,772
Intangible assets with finite lives (amortized), Gross Carrying Amount	775,042	768,932
Intangible assets with finite lives (amortized), Accumulated Amortization	545,012	511,024
Intangible assets with finite lives (amortized), Net Book Value	230,030	257,908
Intangible Assets, Net (Including Goodwill)	1,421,633	1,440,680
Purchased software
Intangible assets with finite lives (amortized), Gross Carrying Amount	365,904	362,955
Intangible assets with finite lives (amortized), Accumulated Amortization	243,809	228,377
Intangible assets with finite lives (amortized), Net Book Value	$ 122,095	134,578
Acquired finite-lived intangible asset, weighted average useful life	9 years
Capitalized software
Intangible assets with finite lives (amortized), Gross Carrying Amount	$ 22,877	22,877
Intangible assets with finite lives (amortized), Accumulated Amortization	22,877	22,877
Intangible assets with finite lives (amortized), Net Book Value	0	0
Customer lists and relationships
Intangible assets with finite lives (amortized), Gross Carrying Amount	362,895	359,932
Intangible assets with finite lives (amortized), Accumulated Amortization	259,569	241,554
Intangible assets with finite lives (amortized), Net Book Value	$ 103,326	118,378
Acquired finite-lived intangible asset, weighted average useful life	10 years
Trademarks and trade names
Intangible assets with finite lives (amortized), Gross Carrying Amount	$ 19,270	19,138
Intangible assets with finite lives (amortized), Accumulated Amortization	14,661	14,186
Intangible assets with finite lives (amortized), Net Book Value	$ 4,609	4,952
Acquired finite-lived intangible asset, weighted average useful life	10 years
Other
Intangible assets with finite lives (amortized), Gross Carrying Amount	$ 4,096	4,030
Intangible assets with finite lives (amortized), Accumulated Amortization	4,096	4,030
Intangible assets with finite lives (amortized), Net Book Value	$ 0	$ 0

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

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- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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- Definition

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.

+ References

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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- Definition

Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance.

+ References

No definition available.

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