Share-based Compensation - Share-Based Compensation Expense Recorded in the Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 1,736	$ 1,318	$ 3,780	$ 2,787
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,574	1,217	3,498	2,575
Research and development and engineering
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	108	54	192	97
Cost of Revenue
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 54	$ 47	$ 90	$ 115