Note 2 - Goodwill and Purchased Intangible Assets - Changes in Carrying Value of Goodwill (Details) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 26, 2021		Dec. 26, 2020
Beginning balance		$ 252,304	[1]	$ 238,669
Impact of currency exchange		(3,828)		13,635
Sale of PCB Test business (1)	[2]	(21,899)
Ending balance		226,577		252,304	[1]
Semiconductor Test and Inspection [Member]
Beginning balance		230,724		218,775
Impact of currency exchange		(4,147)		11,949
Sale of PCB Test business (1)	[2]	0
Ending balance		226,577		230,724
PCB Test [Member]
Beginning balance		21,580		19,894
Impact of currency exchange		319		1,686
Sale of PCB Test business (1)	[2]	(21,899)
Ending balance		$ 0		$ 21,580

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

[2] On June 24, 2021, we completed the sale of our PCB Test business. See Note 12, “Discontinued Operations and Divestitures” for additional information.