Schedule of Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 506,698	$ 414,038
Accumulated Amortization	(365,439)	(337,155)
Foreign Currency Translation Adjustment	(1,296)	2,205
Net Carrying Amount	139,963	79,088
Developed technology
Finite-Lived Intangible Assets
Gross Carrying Amount	336,306	270,877
Accumulated Amortization	(244,833)	(226,190)
Foreign Currency Translation Adjustment	(1,117)	1,618
Net Carrying Amount	90,356	46,305
Customer Relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	105,622	92,741
Accumulated Amortization	(89,848)	(83,585)
Foreign Currency Translation Adjustment	(83)	171
Net Carrying Amount	15,691	9,327
Trademarks and tradenames
Finite-Lived Intangible Assets
Gross Carrying Amount	64,420	50,100
Accumulated Amortization	(30,408)	(27,120)
Foreign Currency Translation Adjustment	(96)	416
Net Carrying Amount	33,916	23,396
Non-compete Agreements
Finite-Lived Intangible Assets
Gross Carrying Amount	320	320
Accumulated Amortization	(320)	(260)
Net Carrying Amount		$ 60
Customer backlog
Finite-Lived Intangible Assets
Gross Carrying Amount	30
Accumulated Amortization	$ (30)