Stockholders' Equity - Estimated Fair Value of ESPP, Valuation Assumptions (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 28, 2020	Mar. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 11,703	$ 8,713
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	42.00%	72.00%
Risk-free interest rate	1.56%	2.48%
Expected life	6 months	6 months
Estimated fair value (in usd per share)	$ 2.17	$ 1.77
Total stock-based compensation expense	$ 1,513	$ 1,316
ESPP \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	70.00%	48.00%
Risk-free interest rate	1.76%	1.90%
Estimated fair value (in usd per share)	$ 1.64	$ 2.47
ESPP \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	72.00%	62.00%
Risk-free interest rate	2.48%	2.31%
Estimated fair value (in usd per share)	$ 1.76	$ 3.13

Share Based Compensation Arrangement by Share Based Payment Award Estimated Fair Value of Common Stock per Share

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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