Stockholders' Equity and Stock-Based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense related to employee stock options and employee stock purchases	$ 2,447	$ 2,000	$ 6,775	$ 5,432
Cost of products [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense related to employee stock options and employee stock purchases	216	116	628	273
Cost of service [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense related to employee stock options and employee stock purchases	161	138	463	355
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense related to employee stock options and employee stock purchases	509	387	1,262	985
Selling [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense related to employee stock options and employee stock purchases	639	537	1,707	1,492
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense related to employee stock options and employee stock purchases	$ 922	$ 822	$ 2,715	$ 2,327