Schedule of Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 29, 2019		Sep. 30, 2018		Sep. 29, 2019		Sep. 30, 2018		Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 582,038		$ 566,848		$ 1,640,315		$ 1,581,244
Income (loss) before income taxes	[1],[2]	151,733		140,844		376,889		356,675
Total assets		2,698,791	[3]	2,882,487	[3]	2,698,791	[3]	2,882,487	[3]	$ 2,706,606
Semiconductor Test
Segment Reporting Information [Line Items]
Revenues		397,737		417,297		1,113,489		1,150,712
Income (loss) before income taxes	[1],[2]	116,633		126,638		291,037		305,876
Total assets	[3]	757,422		709,616		757,422		709,616
System Test
Segment Reporting Information [Line Items]
Revenues		73,305		49,606		204,934		162,308
Income (loss) before income taxes	[1],[2]	24,381		9,056		63,254		35,296
Total assets	[3]	126,452		83,160		126,452		83,160
Industrial Automation
Segment Reporting Information [Line Items]
Revenues		68,892		65,913		209,753		176,803
Income (loss) before income taxes	[1],[2]	(1,645)		940		(10,670)		(1,198)
Total assets	[3]	580,635		617,741		580,635		617,741
Wireless Test
Segment Reporting Information [Line Items]
Revenues		42,264		34,304		112,541		92,023
Income (loss) before income taxes	[1],[2]	11,182		7,843		25,740		18,615
Total assets	[3]	94,789		79,986		94,789		79,986
Corporate And Others [Member]
Segment Reporting Information [Line Items]
Revenues		(160)		(272)		(402)		(602)
Income (loss) before income taxes	[1],[2]	1,182		(3,633)		7,528		(1,914)
Total assets	[3]	$ 1,139,493		$ 1,391,984		$ 1,139,493		$ 1,391,984

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

[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.