Goodwill and Intangible Assets - Goodwill (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 28, 2019	Dec. 29, 2018
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 189,214,000	$ 189,920,000
Foreign currency translation	(655,000)	(706,000)
Goodwill, ending balance	188,559,000	189,214,000
Goodwill impairment	0
Probe Cards
Goodwill [Roll Forward]
Goodwill, beginning balance	172,482,000	172,482,000
Foreign currency translation	0	0
Goodwill, ending balance	172,482,000	172,482,000
Systems
Goodwill [Roll Forward]
Goodwill, beginning balance	16,732,000	17,438,000
Foreign currency translation	(655,000)	(706,000)
Goodwill, ending balance	$ 16,077,000	$ 16,732,000