Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value			$ 1,641,240
Other comprehensive income (loss), net of tax	$ (3,099)	$ 20,463	(9,713)	$ 37,471
Ending balance, Value	1,616,438		1,616,438
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value			(93,319)
Other comprehensive income (loss) before reclassifications, net of tax			(9,863)
Other comprehensive income (loss), net of tax			(9,863)
Ending balance, Value	(103,182)		(103,182)
Unrealized Gains (Losses) on Available-For-Sale Marketable Debt Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value			(178)
Other comprehensive income (loss) before reclassifications, net of tax			150
Other comprehensive income (loss), net of tax			150
Ending balance, Value	(28)		(28)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value			(93,497)
Other comprehensive income (loss) before reclassifications, net of tax			(9,713)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			0
Other comprehensive income (loss), net of tax			(9,713)
Ending balance, Value	$ (103,210)		$ (103,210)