Schedule of Geographic Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Segment Reporting Information [Line Items]
Revenue	$ 154,066	$ 160,794	$ 466,397	$ 458,159
United States
Segment Reporting Information [Line Items]
Revenue	63,278	63,073	190,048	181,653
Germany
Segment Reporting Information [Line Items]
Revenue	21,423	23,089	63,738	64,170
Rest of Europe
Segment Reporting Information [Line Items]
Revenue	30,489	30,222	97,230	80,629
China
Segment Reporting Information [Line Items]
Revenue	11,895	17,516	42,395	51,486
Rest of Asia-Pacific
Segment Reporting Information [Line Items]
Revenue	24,218	24,882	65,367	74,589
Other Countries
Segment Reporting Information [Line Items]
Revenue	$ 2,763	$ 2,012	$ 7,619	$ 5,632