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Changes in Carrying Amount of Goodwill by Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Nov. 14, 2019	Apr. 25, 2018	Feb. 26, 2018
Goodwill [Line Items]
Goodwill acquisition	$ 1,428
Foreign currency translation adjustment		$ (20,531)
Goodwill	1,144,416	1,014,577	$ 1,178,997
Accumulated impairment losses	(762,566)	(762,566)	(762,566)
Goodwill	381,850	252,011	416,431
Mobile Industrial Robots (MiR)
Goodwill [Line Items]
Goodwill acquisition		135,976
Goodwill					$ 135,976
Energid Technologies Corporation
Goodwill [Line Items]
Goodwill acquisition		14,394
Goodwill						$ 14,400
Lemsys
Goodwill [Line Items]
Goodwill acquisition	41,372
Autoguide LLC
Goodwill [Line Items]
Foreign currency translation adjustment	(8,219)
Goodwill				$ 41,372
Industrial Automation
Goodwill [Line Items]
Foreign currency translation adjustment		(20,531)
Goodwill	363,358	233,519	396,483
Accumulated impairment losses	0	0	0
Goodwill	363,358	233,519	396,483
Industrial Automation \| Mobile Industrial Robots (MiR)
Goodwill [Line Items]
Goodwill acquisition		135,976
Industrial Automation \| Energid Technologies Corporation
Goodwill [Line Items]
Goodwill acquisition		14,394
Industrial Automation \| Lemsys
Goodwill [Line Items]
Goodwill acquisition	41,372
Industrial Automation \| Autoguide LLC
Goodwill [Line Items]
Foreign currency translation adjustment	(8,247)
Wireless Test
Goodwill [Line Items]
Goodwill	361,819	361,819	361,819
Accumulated impairment losses	(353,843)	(353,843)	(353,843)
Goodwill	7,976	7,976	7,976
Semiconductor Test
Goodwill [Line Items]
Goodwill acquisition	1,428
Goodwill	260,540	260,540	261,996
Accumulated impairment losses	(260,540)	(260,540)	(260,540)
Goodwill			1,456
Semiconductor Test \| Autoguide LLC
Goodwill [Line Items]
Foreign currency translation adjustment	28
System Test
Goodwill [Line Items]
Goodwill	158,699	158,699	158,699
Accumulated impairment losses	(148,183)	(148,183)	(148,183)
Goodwill	$ 10,516	$ 10,516	$ 10,516