Financial Instruments and Hedging Activities (Summarized Activity of Derivative Instruments) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Document Period End Date			Mar. 31, 2020
Derivatives Not Designated as Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount	$ 54,500		$ 54,500		$ 189,600
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	$ (143)	$ 2,170	$ 442	$ 440