Goodwill and Intangible Assets, net - Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 451,716	$ 444,461
Accum. Amortization	362,792	348,987
Net	88,924	95,474
Customer Lists
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	409,980	403,913
Accum. Amortization	341,387	329,406
Net	68,593	74,507
Trade Names And Other Intangibles
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	41,736	40,548
Accum. Amortization	21,405	19,581
Net	$ 20,331	$ 20,967

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 928
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6473545&loc=d3e61844-108004

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 926
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=120154696&loc=d3e54445-107959

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