Schedule of Segment Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	[2]	$ 2,294,965	[1]	$ 2,100,802	[1]	$ 2,136,606
Income (loss) before taxes	[3],[4]	525,772		467,801		524,411
Total assets	[5]	2,787,014		2,706,606		3,109,545
Property additions		134,642		114,379		105,375
Depreciation and amortization expense		120,655		113,224		108,075
Semiconductor Test
Segment Reporting Information [Line Items]
Revenues		1,552,571		1,492,417		1,662,549
Income (loss) before taxes	[3],[4]	416,973		397,645		491,361
Total assets	[5]	784,808		669,452		597,480
Property additions		112,145		94,496		87,920
Depreciation and amortization expense		59,197		58,095		58,901
System Test
Segment Reporting Information [Line Items]
Revenues		287,455	[1]	216,132	[1]	192,135
Income (loss) before taxes	[3],[4]	93,543		48,857		10,305
Total assets	[5]	131,428		88,098		97,018
Property additions		3,059		3,469		5,976
Depreciation and amortization expense		5,518		6,430		6,646
Industrial Automation
Segment Reporting Information [Line Items]
Revenues		298,139		261,452		170,056
Income (loss) before taxes	[3],[4]	(5,916)		7,670		8,763
Total assets	[5]	671,559		607,502		368,037
Property additions		9,076		11,188		7,044
Depreciation and amortization expense		40,904		36,755		25,711
Wireless Test
Segment Reporting Information [Line Items]
Revenues		157,315	[1]	132,006	[1]	111,866
Income (loss) before taxes	[3],[4]	35,585		29,052		17,350
Total assets	[5]	97,299		77,570		59,912
Property additions		10,362		5,226		4,435
Depreciation and amortization expense		5,365		5,328		5,392
Corporate And Eliminations
Segment Reporting Information [Line Items]
Revenues		(515)		(1,205)
Income (loss) before taxes	[3],[4]	(14,413)		(15,423)		(3,368)
Total assets	[5]	1,101,920		1,263,984		1,987,098
Depreciation and amortization expense		$ 9,671		$ 6,616		$ 11,425

[1] Restructuring and other includes a $5.8 million gain for the decrease in the fair value adjustment to the MiR acquisition contingent consideration, partially offset by a $3.0 million fair value adjustment to increase the AutoGuide acquisition contingent consideration, $0.5 million of employee severance charges and $0.2 million of acquisition related expenses and compensation.

[2] Revenues attributable to a country are based on location of customer site.

[3] Included in Corporate and Other are: contingent consideration adjustments, investment impairment, pension and postretirement plans actuarial gains (losses), severance charges, property insurance recovery related to the Japan earthquake, interest income, interest expense, net foreign exchange gains (losses), intercompany eliminations and acquisition related charges.

[4] Included in income (loss) before taxes are charges and credits related to restructuring and other, and inventory charges. In 2016, loss before income taxes in Wireless Test also included charges related to goodwill and acquired intangible assets impairment.

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