Stock-Based Compensation - Summary of Fair Value of Employee Stock Options Estimated Weighted-average Assumptions (Details) - Stock Options - $ / shares	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	6 years 1 month 6 days	6 years	6 years
Expected volatility	86.50%	83.90%	79.30%
Risk-free interest rate	0.50%	1.10%	2.50%
Weighted average fair value of share-based awards granted	$ 41.1	$ 30.1	$ 1.0

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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- Definition

The 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.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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)
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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