Stock-Based Compensation (Summary of Performance Stock Unit Activity) (Details) - Performance Shares - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Outstanding, beginning balance (in shares)	109,655	75,949	54,505
Granted (in shares)	34,989	33,706	21,444
Vested (in shares)	(43,594)	0	0
Canceled (in shares)	(1,208)	0	0
Outstanding, ending balance (in shares)	99,842	109,655	75,949
Weighted-Average Grant-Date Fair Value
Weighted-Average Grant-Date Fair Value, Outstanding, beginning balance (in dollars per share)	$ 146.96	$ 119.45	$ 108.51
Weighted-Average Grant-Date Fair Value, Granted (in dollars per share)	190.83	238.12	147.25
Weighted-Average Grant-Date Fair Value, Vested (in dollars per share)	128.54
Weighted-Average Grant-Date Fair Value, Canceled (in dollars per share)	228.68
Weighted-Average Grant-Date Fair Value, Outstanding, ending balance (in dollars per share)	$ 162.34	$ 146.96	$ 119.45
Additional Disclosures
Weighted-Average Remaining Contractual Life, Outstanding	1 year 10 months 2 days	1 year 9 months 7 days	1 year 11 months 4 days
Aggregate Intrinsic Value, Outstanding	$ 14,469	$ 12,423	$ 16,263

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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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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 remaining contractual term for equity-based awards excluding options, 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 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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Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

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