Schedule of Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended
		Apr. 01, 2018		Apr. 02, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues		$ 487,467		$ 456,913
Income (loss) before income taxes	[1],[2]	95,820		92,016
Total assets		2,995,193	[3]	2,842,280	[3]	$ 3,109,545
Semiconductor Test
Segment Reporting Information [Line Items]
Revenues		373,328		355,528
Income (loss) before income taxes	[1],[2]	88,079		97,966
Total assets	[3]	758,737		740,334
System Test
Segment Reporting Information [Line Items]
Revenues		43,019		39,845
Income (loss) before income taxes	[1],[2]	5,888		(2,759)
Total assets	[3]	90,785		106,754
Industrial Automation
Segment Reporting Information [Line Items]
Revenues		48,834		36,272
Income (loss) before income taxes	[1],[2]	784		(2,571)
Total assets	[3]	406,557		331,016
Wireless Test
Segment Reporting Information [Line Items]
Revenues		22,507		25,268
Income (loss) before income taxes	[1],[2]	464		1,532
Total assets	[3]	59,739		61,356
Corporate and Other
Segment Reporting Information [Line Items]
Revenues		(221)
Income (loss) before income taxes	[1],[2]	605		(2,152)
Total assets	[3]	$ 1,679,375		$ 1,602,820

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