Stockholders' Equity and Stock-Based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
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	$ 3,212	$ 2,447	$ 8,229	$ 6,775
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	224	216	455	628
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	223	161	564	463
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	744	509	1,727	1,262
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	779	639	2,049	1,707
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	$ 1,242	$ 922	$ 3,434	$ 2,715