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Stock Plans and Stock-Based Compensation - Assumptions used to Calculate Fair Value of Stock-Based Compensation (Details) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Expected term (in years) | 10 years |  |
Dividend yield | 0.00% |  |
Employee Stock Option |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Risk-free interest rate, minimum | 0.40% | 1.60% | 1.20%
Risk-free interest rate, maximum | 0.50% | 2.30% | 3.10%
Expected term (in years) | 6 years 7 days | 6 years 7 days |
Volatility, minimum | 76.50% | 71.80% | 58.70%
Volatility, maximum | 78.50% | 74.60% | 75.50%
Dividend yield | 0.00% | 0.00% | 0.00%
ESPP |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Risk-free interest rate, minimum | 0.10% | 1.60% | 2.10%
Risk-free interest rate, maximum | 0.20% | 2.30% | 2.60%
Volatility, minimum | 66.60% | 64.80% | 54.30%
Volatility, maximum | 136.00% | 77.10% | 65.50%
Dividend yield | 0.00% | 0.00% | 0.00%
Minimum | Employee Stock Option |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Expected term (in years) |  |  | 5 years 1 month 28 days
Minimum | ESPP |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Expected term (in years) | 6 months | 6 months | 6 months
Maximum | Employee Stock Option |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Expected term (in years) |  |  | 9 years 11 months 12 days
Maximum | ESPP |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |
Expected term (in years) | 2 years | 2 years | 2 years

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- Definition 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. + References No definition available. + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the maximum 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. + References No definition available. + Details
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- Definition The estimated measure of the minimum 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. + References No definition available. + Details
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- Definition The maximum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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- Definition The minimum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
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