Financial Instruments and Hedging Activities (Summarized Activity of Derivative Instruments) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Document Period End Date			Mar. 31, 2019
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	$ 2,170	$ (785)	$ 440	$ (1,182)