Stock-Based Compensation (Summary of Restricted Stock Unit and Performance Based Restricted Stock Unit Activity) (Details) shares in Thousands	9 Months Ended
Sep. 30, 2021 $ / shares shares
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding at December 31, 2020 \| shares	274
Number of Shares, Granted \| shares	107
Number of Shares, Vested \| shares	(128)
Number of Shares, Forfeited/canceled \| shares	(8)
Number of Shares, Outstanding at September 30, 2021 \| shares	245
Weighted-Average Grant Date Fair Value per Share, Outstanding at December 31, 2020 \| $ / shares	$ 206.48
Weighted-Average Grant Date Fair Value per Share, Granted \| $ / shares	240.07
Weighted-Average Grant Date Fair Value per Share, Vested \| $ / shares	187.29
Weighted-Average Grant Date Fair Value per Share, Forfeited/canceled \| $ / shares	234.45
Weighted-Average Grant Date Fair Value per Share, Outstanding at September 30, 2021 \| $ / shares	$ 230.28
Performance Stock Units (PSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding at December 31, 2020 \| shares	148
Number of Shares, Granted \| shares	154
Number of Shares, Vested \| shares
Number of Shares, Forfeited/canceled \| shares	(5)
Number of Shares, Outstanding at September 30, 2021 \| shares	297
Weighted-Average Grant Date Fair Value per Share, Outstanding at December 31, 2020 \| $ / shares	$ 376.48
Weighted-Average Grant Date Fair Value per Share, Granted \| $ / shares	236.70
Weighted-Average Grant Date Fair Value per Share, Vested \| $ / shares
Weighted-Average Grant Date Fair Value per Share, Forfeited/canceled \| $ / shares	340.32
Weighted-Average Grant Date Fair Value per Share, Outstanding at September 30, 2021 \| $ / shares	$ 304.47
Performance period	3 years

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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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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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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