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Changes in Carrying Amount of Goodwill by Segment (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Apr. 25, 2018	Feb. 26, 2018	Dec. 31, 2017
Goodwill [Line Items]
Foreign currency translation adjustment	$ (8,144)
Goodwill	1,155,564			$ 1,014,577
Accumulated impairment losses	(762,566)			(762,566)
Goodwill	392,998			252,011
Mobile Industrial Robots (MiR)
Goodwill [Line Items]
Goodwill acquisition	134,737
Goodwill		$ 134,737
Energid Technologies Corporation
Goodwill [Line Items]
Goodwill acquisition	14,394
Goodwill			$ 14,400
Wireless Test
Goodwill [Line Items]
Goodwill	361,819			361,819
Accumulated impairment losses	(353,843)			(353,843)
Goodwill	7,976			7,976
Industrial Automation
Goodwill [Line Items]
Foreign currency translation adjustment	(8,144)
Goodwill	374,506			233,519
Goodwill	374,506			233,519
Industrial Automation \| Mobile Industrial Robots (MiR)
Goodwill [Line Items]
Goodwill acquisition	134,737
Industrial Automation \| Energid Technologies Corporation
Goodwill [Line Items]
Goodwill acquisition	14,394
System Test
Goodwill [Line Items]
Goodwill	158,699			158,699
Accumulated impairment losses	(148,183)			(148,183)
Goodwill	10,516			10,516
Semiconductor Test
Goodwill [Line Items]
Goodwill	260,540			260,540
Accumulated impairment losses	$ (260,540)			$ (260,540)