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Stock-Based Compensation - Weighted-Average Assumptions Used to Estimate the Fair Value of Options Granted (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.83%	2.29%	2.76%
Expected term	6 years 1 month 9 days	6 years 25 days	6 years 3 months 7 days
Expected volatility	58.00%	61.00%	63.00%
Expected dividends	0.00%	0.00%	0.00%
Options | Weighted Average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share (usd per share)	$ 19.30	$ 11.35	$ 9.33
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.14%	1.95%
Expected term	6 months	6 months
Expected volatility	54.00%	53.00%
Expected dividends	0.00%	0.00%
ESPP | Weighted Average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share (usd per share)	$ 32.18	$ 5.98

X

- 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

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

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

+ 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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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

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

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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

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-Publisher FASB
-Name Accounting Standards Codification
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