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Stock-Based Compensation - Valuation Assumptions Used to Estimate Grant-Date Fair Value (Details)
3 Months Ended 9 Months Ended
Sep. 28, 2018
Sep. 29, 2017
Sep. 28, 2018
Sep. 29, 2017
Stock options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Risk-free interest rate 2.91% 1.70% 2.83% 1.68%
Dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility 55.00% 58.00% 55.00% 61.00%
Expected life 4 years 5 months 8 days 3 years 11 months 23 days 4 years 5 months 1 day 4 years 1 month 24 days
ESPP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Risk-free interest rate 2.11% 1.14% 1.74% 0.88%
Dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility 51.00% 55.00% 52.00% 61.00%
Expected life 6 months 6 months 6 months 6 months