Stock-Based Compensation - Valuation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Non-cash stock-based compensation expense recognized	$ 64,954	$ 14,262	$ 36,261
Black-Scholes option valuation model, assumptions
Dividend yield (as a percent)	0.00%
Stock options \| Minimum
Black-Scholes option valuation model, assumptions
Risk free interest rate (as a percent)	0.17%	1.51%	2.09%
Volatility factor (as a percent)	28.91%	28.86%	23.33%
Expected term of options	3 years 3 months 18 days	4 years 3 months 18 days	2 years 9 months 18 days
Fair value of options granted (in dollars per share)	$ 5.50	$ 7.58	$ 7.10
Stock options \| Maximum
Black-Scholes option valuation model, assumptions
Risk free interest rate (as a percent)	1.72%	2.53%	2.98%
Volatility factor (as a percent)	48.08%	32.08%	30.22%
Expected term of options	5 years 6 months	5 years 6 months	5 years 6 months
Fair value of options granted (in dollars per share)	$ 12.10	$ 12.45	$ 12.53

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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

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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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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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