Schedule of Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Oct. 01, 2017		Sep. 30, 2018		Oct. 01, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues		$ 566,848		$ 503,378		$ 1,581,244		$ 1,657,191
Income (loss) before income taxes	[1],[2]	140,844		127,437		356,675		426,329
Total assets		2,882,487	[3]	3,089,327	[3]	2,882,487	[3]	3,089,327	[3]	$ 3,109,545
Semiconductor Test
Segment Reporting Information [Line Items]
Revenues		417,297		396,881		1,150,712		1,345,560
Income (loss) before income taxes	[1],[2]	126,638		116,836		305,876		426,081
Total assets	[3]	709,616		598,925		709,616		598,925
System Test
Segment Reporting Information [Line Items]
Revenues		65,913		40,063		176,803		115,672
Income (loss) before income taxes	[1],[2]	940		3,373		(1,198)		(279)
Total assets	[3]	617,741		508,943		617,741		508,943
Industrial Automation
Segment Reporting Information [Line Items]
Revenues		49,606		35,569		162,308		112,147
Income (loss) before income taxes	[1],[2]	9,056		(3,344)		35,296		(11,795)
Total assets	[3]	83,160		100,083		83,160		100,083
Wireless Test
Segment Reporting Information [Line Items]
Revenues		34,304		30,865		92,023		83,812
Income (loss) before income taxes	[1],[2]	7,843		7,461		18,615		13,508
Total assets	[3]	79,986		61,206		79,986		61,206
Corporate and Eliminations
Segment Reporting Information [Line Items]
Revenues		(272)				(602)
Income (loss) before income taxes	[1],[2]	(3,633)		3,111		(1,914)		(1,186)
Total assets	[3]	$ 1,391,984		$ 1,820,170		$ 1,391,984		$ 1,820,170

[1] Included in Corporate and Other are: contingent consideration adjustments, severance charges, interest income, interest expense, net foreign exchange gains (losses), intercompany eliminations and acquisition related charges.

[2] Included in the income (loss) before income taxes for each of the segments are charges and credits related to restructuring and other and inventory charges.

[3] Total business assets are directly attributable to each business. Corporate assets consist of cash and cash equivalents, marketable securities and certain other assets.