Schedule of Geographic Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 28, 2018	Sep. 29, 2017
Segment Reporting Information [Line Items]
Revenue	$ 160,794	$ 146,296	$ 458,159	$ 374,372
UNITED STATES
Segment Reporting Information [Line Items]
Revenue	63,073	58,949	181,653	157,778
GERMANY
Segment Reporting Information [Line Items]
Revenue	23,089	17,728	64,170	46,807
Rest Of Europe
Segment Reporting Information [Line Items]
Revenue	30,222	27,152	80,629	55,164
CHINA
Segment Reporting Information [Line Items]
Revenue	17,516	15,459	51,486	40,920
Rest of Asia-Pacific
Segment Reporting Information [Line Items]
Revenue	24,882	23,769	74,589	64,511
Other Countries
Segment Reporting Information [Line Items]
Revenue	$ 2,012	$ 3,239	$ 5,632	$ 9,192