Share-based Compensation Arrangement by Share-based Payment Award, Performance Metric Target Amount, Percentage

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Share-based Compensation Arrangement by Share-based Payment Award, Vested but Unexercised Options Forfeiture Period after Employee has Ended

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

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Aggregate number of common shares reserved for future issuance.

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Amount of cost capitalized for award under share-based payment arrangement.

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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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Amount of cost to be recognized for option under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from issuance of shares under share-based payment arrangement. Excludes option exercised.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Amount of additional cost recognized for award under share-based payment arrangement from occurrence of event accelerating recognition of cost.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

Discount rate from fair value on offering date that participants pay for shares.

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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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- Definition

Number of shares authorized for issuance under share-based payment arrangement.

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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 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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Number of shares issued under share-based payment arrangement.

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Price of a single share of a number of saleable stocks of a company.

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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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Stock-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	May 23, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 14, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture period once emplyment has ended		90 days
Accelerated compensation cost			$ 18,500
Weighted-average fair value of options granted		$ 41.09	$ 33.99	$ 33.01
Total intrinsic value for options exercised		$ 235,000	$ 132,800	$ 78,000
Cash received from option exercises		142,500	136,000	74,700
Tax benefit realized from stock option exercises		$ 16,900	10,200
Share price		$ 282.13
Total fair value of shares vested		$ 28,800	26,500	24,000
Non-cash compensation expense		68,890	73,214	42,327
Non-cash compensation capitalized to fixed and intangible assets		1,500	1,100	800
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested stock options		$ 15,100
Weighted average period to recognize cost		1 year 9 months 18 days
Performance Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Performance period		3 years
2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares remaining available for future issuance under the plan		234,762
Non-cash compensation expense		$ 1,100	$ 1,000	$ 600
2008 Plan [Member] \| Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Class A common stock issued under the purchase plan				16,798
Cash proceeds from issuance of shares under the purchase plan				$ 2,300
2018 Plan [Member] \| Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares remaining available for future issuance under the plan	300,000
Percentage of purchase plan price per share equal to the fair market value	85.00%
Class A common stock issued under the purchase plan		25,058	30,128
Cash proceeds from issuance of shares under the purchase plan		$ 6,100	$ 5,500
2020 Plan [Member] \| Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuance of shares					3,000,000.0
Shares remaining available for future issuance under the plan		3,000,000.0
Minimum [Member] \| Performance Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance metric, target amount, percentage		0.00%
Maximum [Member] \| Performance Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance metric, target amount, percentage		200.00%