Note 14 - Guarantees - Changes in Accrued Warranty (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 26, 2021	Jun. 27, 2020	Jun. 26, 2021	Jun. 27, 2020
Balance at beginning of period		$ 7,138	$ 6,268	$ 6,382	$ 6,155
Warranty expense accruals		3,243	1,044	5,652	2,935
Warranty payments		(1,895)	(1,316)	(3,548)	(3,094)
Liability transferred (1)	[1]	(945)	0	(945)	0
Balance at end of period		$ 7,541	$ 5,996	$ 7,541	$ 5,996

[1] Warranty liability transferred in connection with the sale of our PCB Test business.