Financial Instruments and Hedging Activities (Summarized Activity of Derivative Instruments) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Document Period End Date			Jun. 30, 2019
Derivatives Not Designated as Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount	$ 153,300		$ 153,300		$ 117,100
Derivatives Not Designated as Hedges | Foreign currency forward contracts | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	$ (799)	$ (1,597)	$ (359)	$ (2,381)