Employee Benefit Plans and Stock-based Compensation - Summary of Projected Benefit Obligation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 28, 2018	Sep. 29, 2017
Employee Benefits and Share-based Compensation, Noncash [Abstract]
Service cost	$ 59	$ 55	$ 185	$ 165
Interest cost	18	16	56	48
Recognized net actuarial loss	0	1	0	4
Net periodic benefit cost included in operating loss	$ 77	$ 72	$ 241	$ 217