Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance, Value			$ 1,641,240
Other comprehensive income (loss), net of tax	$ (29,721)	$ 11,504	(6,614)	$ 17,008
Ending balance, Value	1,599,594		1,599,594
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			(6,721)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			0
Other comprehensive income (loss), net of tax			(6,721)
Ending balance, Value	(100,040)		(100,040)
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			107
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			0
Other comprehensive income (loss), net of tax			107
Ending balance, Value	(71)		(71)
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			(6,614)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			0
Other comprehensive income (loss), net of tax			(6,614)
Ending balance, Value	$ (100,111)		$ (100,111)