Note 10 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020	Dec. 26, 2020
Net sales		$ 225,063	$ 150,647	$ 695,354	$ 433,652
Profit (loss) for reportable segments		36,345	(2,384)	117,480	(13,283)
Gain (Loss) on Disposition of Business	[1]	90	(0)	75,754	(0)
Interest expense		(966)	(3,021)	(5,372)	(10,904)
Interest income		53	42	197	210
Gain (Loss) on Extinguishment of Debt, Total		(1,650)	293	(3,411)	293
Income (loss) from continuing operations before taxes		31,125	(5,530)	175,062	(28,443)
Total assets for reportable segments		1,272,868		1,272,868		$ 1,090,346	[2]
Corporate, Non-Segment [Member]
Corporate expenses		(2,747)	(460)	(9,586)	(4,759)
Total assets for reportable segments		131,802		131,802		55,492
Semiconductor Test and Inspection [Member]
Net sales		225,063	137,225	668,594	396,666
Profit (loss) for reportable segments		36,345	(4,093)	113,573	(17,997)
Total assets for reportable segments		1,141,066		1,141,066		968,028
PCB Test [Member]
Net sales		0	13,422	26,760	36,986
Profit (loss) for reportable segments		0	$ 1,709	3,907	$ 4,714
Total assets for reportable segments		0		0		66,826
Semiconductor Test and Inspection and PCB Test [Member]
Total assets for reportable segments		$ 1,141,066		$ 1,141,066		$ 1,034,854

[1] On June 24, 2021 we completed the divestment of our PCB Test business. The divestment of this business did not qualify for presentation as discontinued operations and the results of the PCB Test business are included in continuing operations for all periods presented. See Note 12, “Business Divestitures and Discontinued Operations” for additional information on this transaction and financial statement presentation.

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