Note 14 - Guarantees - Changes in Accrued Warranty (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020
Balance at beginning of period		$ 7,541	$ 5,996	$ 6,382	$ 6,155
Warranty expense accruals		4,148	911	9,800	3,846
Warranty payments		(3,005)	(1,169)	(6,553)	(4,263)
Liability transferred (1)	[1]	0	0	(945)	0
Balance at end of period		$ 8,684	$ 5,738	$ 8,684	$ 5,738

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