Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 26, 2020	Dec. 28, 2019
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 199,196	$ 189,214
Foreign currency translation	1,067	(166)
Goodwill, ending balance	220,757	199,196
FRT GmbH
Goodwill [Roll Forward]
Goodwill, Acquired During Period	975	10,148
Baldwin Park
Goodwill [Roll Forward]
Goodwill, Acquired During Period	19,519
Probe Cards
Goodwill [Roll Forward]
Goodwill, beginning balance	172,482	172,482
Foreign currency translation	0	0
Goodwill, ending balance	192,001	172,482
Probe Cards | FRT GmbH
Goodwill [Roll Forward]
Goodwill, Acquired During Period	0	0
Probe Cards | Baldwin Park
Goodwill [Roll Forward]
Goodwill, Acquired During Period	19,519
Systems
Goodwill [Roll Forward]
Goodwill, beginning balance	26,714	16,732
Foreign currency translation	1,067	(166)
Goodwill, ending balance	28,756	26,714
Systems | FRT GmbH
Goodwill [Roll Forward]
Goodwill, Acquired During Period	975	$ 10,148
Systems | Baldwin Park
Goodwill [Roll Forward]
Goodwill, Acquired During Period	$ 0