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Equity Plans - Employee Stock Options Valuation Assumptions (Details) - Options to purchase common stock	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Plans
Expected volatility, Minimum	72.10%	61.00%	62.00%
Expected volatility, Maximum	87.50%	64.80%	66.50%
Risk-free interest rate, Minimum	0.23%	1.42%	2.42%
Risk-free interest rate, Maximum	1.44%	2.58%	3.03%
Minimum
Equity Plans
Expected term	5 years 3 months 7 days	5 years	5 years 5 months 26 days
Maximum
Equity Plans
Expected term	6 years 29 days	6 years 29 days	6 years 29 days

X

- 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

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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

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- Definition

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

+ References

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- Definition

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

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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.

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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
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