Derivative Instruments - Outstanding Forward Contracts Table (Detail) - Not Designated as Hedging Instrument € in Thousands, ₩ in Thousands, ¥ in Thousands, $ in Thousands, $ in Thousands, $ in Thousands, $ in Thousands	Sep. 30, 2018 CAD ($)	Sep. 30, 2018 SGD ($)	Sep. 30, 2018 JPY (¥)	Sep. 30, 2018 KRW (₩)	Sep. 30, 2018 TWD ($)	Sep. 30, 2018 EUR (€)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2017 SGD ($)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2017 KRW (₩)	Dec. 31, 2017 TWD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 USD ($)
Euro Member Countries, Euro
Derivative [Line Items]
Outstanding forward contracts						€ 19,500	$ 22,602						€ 0	$ 0
Japanese Yen
Derivative [Line Items]
Outstanding forward contracts			¥ 455,000				4,018			¥ 455,000				4,049
United Kingdom, Pounds
Derivative [Line Items]
Outstanding forward contracts			2,100				2,742			1,650				2,232
Hungary, Forint
Derivative [Line Items]
Outstanding forward contracts			¥ 700,000				2,513			¥ 545,000				2,110
Korean Won
Derivative [Line Items]
Outstanding forward contracts				₩ 2,050,000			1,847				₩ 1,825,000			1,708
Taiwanese Dollar
Derivative [Line Items]
Outstanding forward contracts					$ 49,000		1,615					$ 37,725		1,278
Canada, Dollars
Derivative [Line Items]
Outstanding forward contracts	$ 800						616	$ 0						0
Singapore Dollar
Derivative [Line Items]
Outstanding forward contracts		$ 760					557		$ 0					0
Switzerland, Francs
Derivative [Line Items]
Outstanding forward contracts		$ 0					$ 0					$ 1,365		$ 1,401