Stockholders' Equity - Fair Value of Each Option Awarded (Details) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation
Dividend yield (as a percent)	0.00%
Stock Option
Share-Based Compensation
Expected volatility, minimum (as a percent)	61.56%	61.36%	57.95%
Expected volatility, maximum (as a percent)	62.27%	63.28%	60.56%
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected term (in years)			6 years 3 months
Risk-free interest rate, minimum (as a percent)	0.27%	1.69%	2.69%
Risk-free interest rate, maximum (as a percent)	1.34%	2.55%	2.85%
Stock Option \| Minimum
Share-Based Compensation
Fair value of common stock (in dollars per share)	$ 21.13	$ 22.99	$ 37.20
Expected term (in years)	5 years 8 months 19 days	5 years 6 months 10 days
Stock Option \| Maximum
Share-Based Compensation
Fair value of common stock (in dollars per share)	$ 23.99	$ 37.78	$ 58.15
Expected term (in years)	6 years 6 months 14 days	6 years 2 months 4 days

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.

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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.

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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.

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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.

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- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

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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
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Section S99
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-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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