Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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

Restructuring Expenses - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($) position	Sep. 30, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 4,471,000	$ 0
Number of positions reduced \| position		79
Facilities charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 1,729,000
Employee separation
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 2,742,000