Note 10 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 26, 2020		Sep. 26, 2020	[1]	Jun. 27, 2020	[1]	Mar. 28, 2020	[1]	Dec. 28, 2019		Sep. 28, 2019	[1]	Jun. 29, 2019	[1]	Mar. 30, 2019	[1]	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Net sales	$ 202,355	[1]	$ 150,647		$ 144,084		$ 138,921		$ 142,011	[1]	$ 143,498		$ 150,011		$ 147,809		$ 636,007	$ 583,329	$ 451,768
Profit (loss) for reportable segments																	4,474	(42,437)	(2,665)
Interest expense																	(13,759)	(20,556)	(4,977)
Interest income																	224	764	1,187
Gain on extinguishment of debt																	268	0	0
Loss from continuing operations before taxes																	(13,177)	(72,077)	(31,912)
Depreciation																	14,000	19,300	8,800
Total depreciation and amortization																	52,746	58,871	26,047
Capital expenditures																	18,660	18,000	4,967
Assets, Total	1,090,346								1,077,710								1,090,346	1,077,710	1,134,002
Discontinued operations	0								3,618								0	3,618	3,820
Corporate, Non-Segment [Member]
Corporate expenses																	(4,384)	(9,848)	(25,457)
Assets, Total	55,492								18,398								55,492	18,398	34,367
Semiconductor Test and Inspection [Member]
Net sales																	585,240	540,878	443,276
Profit (loss) for reportable segments																	(2,497)	(45,072)	2,489
Depreciation																	51,548	56,621	24,634
Capital expenditures																	18,616	17,831	4,957
Assets, Total	968,028								998,756								968,028	998,756	1,038,053
PCB Test [Member]
Net sales																	50,767	42,451	8,492
Profit (loss) for reportable segments																	6,971	2,635	(5,154)
Depreciation																	1,198	2,250	1,413
Capital expenditures																	44	169	10
Assets, Total	66,826								56,938								66,826	56,938	57,762
Semiconductor Test and Inspection and PCB Test [Member]
Assets, Total	$ 1,034,854								$ 1,055,694								$ 1,034,854	$ 1,055,694	$ 1,095,815

[1] All quarters presented above were comprised of 13 weeks.