Stock-Based Compensation - Assumptions for Stock Option Awards (Details) - Stock option awards	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation assumptions
Volatility, minimum (percent)	57.00%	49.00%	49.00%
Volatility, maximum (percent)	57.00%	55.00%	50.00%
Risk-free interest rate, minimum (percent)	1.68%	2.37%	1.85%
Risk-free interest rate, maximum (percent)	2.55%	3.01%	2.02%
Dividend yield (percent)	0.00%	0.00%	0.00%
Minimum
Valuation assumptions
Expected life (in years)	5 years 5 months 12 days	5 years 3 months 25 days	5 years 7 months 24 days
Maximum
Valuation assumptions
Expected life (in years)	5 years 6 months 14 days	5 years 6 months 29 days	5 years 8 months 1 day

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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.

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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.

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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.

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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.

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No definition available.

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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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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.

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