Goodwill and Intangible Assets Goodwill (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 0
Goodwill		$ 189,920,000	$ 188,010,000	$ 30,731,000
Goodwill, Acquired During Period			158,141,000
Goodwill, Foreign Currency Translation Gain (Loss)		1,910,000	(862,000)
Probe Cards
Goodwill [Line Items]
Goodwill		172,482,000	172,482,000	30,731,000
Goodwill, Acquired During Period			141,751,000
Goodwill, Foreign Currency Translation Gain (Loss)		0	0
Systems
Goodwill [Line Items]
Goodwill		17,438,000	15,528,000	$ 0
Goodwill, Acquired During Period			16,390,000
Goodwill, Foreign Currency Translation Gain (Loss)		$ 1,910,000	$ (862,000)