Business Acquisitions (Detail) - USD ($) $ in Thousands	Nov. 30, 2016	Nov. 04, 2016	Jun. 28, 2016	Nov. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Cash acquired				$ 5,015
Net tangible assets	$ 11,300			4,025
Net deferred taxes				(582)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	123,100
Goodwill				60,494	$ 909,811	$ 801,406	$ 596,316
Total purchase price				$ 97,496
Armasight, Inc. [Member]
Business Acquisition [Line Items]
Cash acquired					2,804
Other tangible assets and liabilities, net					1,925
Net deferred taxes					(1,855)
Identifiable intangible assets					7,600
Goodwill					32,994
Total purchase price			$ 43,468
DVTEL [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles					$ 27,400
Point Grey Research, Inc. [Member]
Business Acquisition [Line Items]
Cash acquired		$ 2,994
Other tangible assets and liabilities, net		35,127
Net deferred taxes		(2,438)
Identifiable intangible assets		39,800
Goodwill		183,678
Total purchase price		$ 259,161
Prox Dynamics, AS [Member]
Business Acquisition [Line Items]
Cash acquired	11,706
Net tangible assets	(900)
Net deferred taxes	(4,250)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	31,400
Goodwill	96,431
Total purchase price	$ 134,387