Note 2 - Goodwill and Purchased Intangible Assets - Changes in Carrying Value of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 27, 2021		Dec. 26, 2020
Beginning balance	$ 252,304	[1]	$ 238,669
Impact of currency exchange	(5,569)		13,635
Ending balance	246,735		252,304	[1]
Semiconductor Test and Inspection [Member]
Beginning balance	230,724		218,775
Impact of currency exchange	(5,109)		11,949
Ending balance	225,615		230,724
PCB Test [Member]
Beginning balance	21,580		19,894
Impact of currency exchange	(460)		1,686
Ending balance	$ 21,120		$ 21,580

[1] Derived from December 26, 2020 audited financial statements