Goodwill and Acquired Intangible Assets (Goodwill and Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Goodwill (not amortized), Net Book Value	$ 1,182,457	$ 1,182,772	$ 1,169,813
Intangible assets with finite lives (amortized), Gross Carrying Amount	766,199	768,932
Intangible assets with finite lives (amortized), Accumulated Amortization	565,997	511,024
Intangible assets with finite lives (amortized), Net Book Value	200,202	257,908
Total goodwill and acquired intangible assets	1,382,659	1,440,680
Purchased Software [Member]
Intangible assets with finite lives (amortized), Gross Carrying Amount	362,679	362,955
Intangible assets with finite lives (amortized), Accumulated Amortization	254,059	228,377
Intangible assets with finite lives (amortized), Net Book Value	$ 108,620	134,578
Weighted average useful lives (in years)	9 years
Capitalized Software [Member]
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 [Member]
Intangible assets with finite lives (amortized), Gross Carrying Amount	357,586	359,932
Intangible assets with finite lives (amortized), Accumulated Amortization	270,272	241,554
Intangible assets with finite lives (amortized), Net Book Value	$ 87,314	118,378
Weighted average useful lives (in years)	10 years
Trademarks And Trade Names [Member]
Intangible assets with finite lives (amortized), Gross Carrying Amount	$ 19,054	19,138
Intangible assets with finite lives (amortized), Accumulated Amortization	14,786	14,186
Intangible assets with finite lives (amortized), Net Book Value	$ 4,268	4,952
Weighted average useful lives (in years)	11 years
Other [Member]
Intangible assets with finite lives (amortized), Gross Carrying Amount	$ 4,003	4,030
Intangible assets with finite lives (amortized), Accumulated Amortization	4,003	4,030
Intangible assets with finite lives (amortized), Net Book Value	$ 0	$ 0

Acquired intangible assets net including goodwill

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- Definition

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.

+ References

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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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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