Goodwill and Intangible Assets, Net - Amortization Expense on Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Cost of revenue	$ 1,405	$ 1,609	$ 1,609
Amortization of definite-lived purchased intangible assets	108,453	96,465	65,017
Total	$ 109,858	$ 98,074	$ 66,626

The amount of expense recognized in the current period that reflects the allocation of the costs of intangible assets over the expected benefit period of such assets. This element applies only to intangible assets used in the delivery of services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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