Stock-Based Compensation - Summary of Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, beginning of year, Weighted-Average Exercise Price (in dollars per share)	$ 67.49	$ 62.80	$ 59.17
Granted, Weighted-Average Exercise Price (in dollars per share)	0	0	0
Exercised, Weighted-Average Exercise Price (in dollars per share)	54.43	53.53	50.92
Forfeited, Weighted-Average Exercise Price (in dollars per share)	0	64.21	86.28
Outstanding, end of year, Weighted-Average Exercise Price (in dollars per share)	74.26	67.49	62.80
Vested and Exercisable, end of year, Weighted-Average Exercise Price (in dollars per share)	74.26	65.71	59.69
Nonvested, Weighted-Average Exercise Price (in dollars per share)	$ 0	$ 94.77	$ 93.44
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of year, Options (in shares)	984	1,484	2,170
Granted, Options (in shares)	0	0	0
Exercised, Options (in shares)	(336)	(495)	(679)
Forfeited, Options (in shares)	0	(5)	(7)
Outstanding, end of year, Options (in shares)	648	984	1,484
Vested and Exercisable, end of year, Options (in shares)	648	924	1,347
Nonvested, Options (in shares)	0	60	137
Outstanding, Weighted-Average Remaining Contractual Term (in years)	2 years 11 months 4 days	3 years 2 months 4 days	3 years 6 months 18 days
Vested and Exercisable, Weighted-Average Remaining Contractual Term (in years)	2 years 11 months 4 days	2 years 11 months 12 days	3 years 1 month 20 days
Nonvested, Weighted-Average Remaining Contractual Term (in years)	0 years	6 years 8 months 15 days	7 years 7 months 6 days
Exercised, Aggregate Intrinsic Value	$ 78,269	$ 72,098	$ 78,648
Outstanding, Aggregate Intrinsic Value	187,679	186,926	118,908
Vested and Exercisable, Aggregate Intrinsic Value	187,679	177,111	112,133
Nonvested, Aggregate Intrinsic Value	0	9,815	6,775
Compensation Expense - Stock Options (in thousands)	$ 1,030	$ 1,709	$ 2,006

Amount by which current fair value of underlying stock exceeds exercise price of nonvested options.

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Weighted average remaining contractual term for nonvested options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of non-vested options outstanding.

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Weighted average grant-date fair value of non-vested options outstanding.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of share options (or share units) exercised during the current period.

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