Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets - Purchase Price Allocation, Xcerra Acquisition (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 28, 2019	Dec. 29, 2018	[1]	Oct. 01, 2018	Dec. 30, 2017
Goodwill		$ 235,903	$ 242,127			$ 65,613
Goodwill, adjustment	[2],[3]	1,134
Xcerra [Member]
Current assets, including cash received		375,990			$ 375,990
Property, plant and equipment		40,729			40,729
Other assets		1,051			2,109
Other assets, adjustment	[4]	(1,058)
Intangible assets		321,160			321,160
Goodwill		180,397			179,263
Goodwill, adjustment	[4]	1,134
Total assets acquired		919,327			919,251
Liabilities assumed		(124,897)			(124,821)
Liabilities assumed, adjustment	[4]	(76)
Net assets acquired		$ 794,430			$ 794,430

[1] Derived from December 29, 2018 audited financial statements

[2] After the acquisition of Xcerra on October 1, 2018 we report in two segments, Semiconductor Test & Inspection and PCB Test. Prior year amounts would have been reported in our Semiconductor Test & Inspection segment and have been presented accordingly.

[3] Amounts represent adjustments made during the post-acquisition measurement period to the preliminary goodwill from the Xcerra acquisition.

[4] Measurement period adjustments made as a result of obtaining new facts and circumstances related to certain assets acquired and liabilities assumed as of the date of acquisition. The net impact of the measurement period adjustments were offset against goodwill.