Goodwill and Intangible Assets, Net - Amortization Expense on Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Cost of revenue	$ 572	$ 1,405	$ 1,609
Amortization of definite-lived purchased intangible assets	105,213	108,453	96,465
Total	$ 105,785	$ 109,858	$ 98,074

Amount of expense for allocation of cost of intangible asset over its useful life directly used in production of good and rendering of service.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(b)(2))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration