Stock-Based Compensation - Assumptions Used to Calculate Fair Value of Awards (Details) - Performance-Based Stock Units - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value	$ 12,266	$ 6,211	$ 5,321
Risk-free rate	1.42%	2.53%	2.37%
Volatility	18.40%	20.70%	22.60%
Expected term	2 years 10 months 24 days	2 years 9 months 18 days	2 years 10 months 24 days
Dividend yield	0.00%	0.00%	0.00%
Unrecognized compensation cost	$ 6,406	$ 4,315	$ 2,739
Term over which compensation cost recognized (in years)	3 years	3 years	3 years

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for 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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- 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 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.

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No definition available.

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- Definition

Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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