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Changes in Carrying Amount of Goodwill by Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Jun. 30, 2019
Goodwill [Line Items]
Goodwill acquisition	$ 1,428
Foreign currency translation adjustment	658
Goodwill	1,144,416	$ 1,146,502
Accumulated impairment losses	(762,566)	(762,566)
Goodwill	381,850	383,936
Industrial Automation
Goodwill [Line Items]
Foreign currency translation adjustment	626
Goodwill	363,358	363,984
Accumulated impairment losses	0	0
Goodwill	363,358	363,984
Wireless Test
Goodwill [Line Items]
Goodwill	361,819	361,819
Accumulated impairment losses	(353,843)	(353,843)
Goodwill	7,976	7,976
Semiconductor Test
Goodwill [Line Items]
Goodwill acquisition	1,428
Foreign currency translation adjustment	32
Goodwill	260,540	262,000
Accumulated impairment losses	(260,540)	(260,540)
Goodwill		1,460
System Test
Goodwill [Line Items]
Goodwill	158,699	158,699
Accumulated impairment losses	(148,183)	(148,183)
Goodwill	$ 10,516	$ 10,516

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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