Share-Based Compensation and Benefit Plans (Restricted Stock Activity) (Details) - Restricted stock [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation and Benefit Plans
Compensation expense for share-based compensation	$ 1,488	$ 1,387	$ 1,370
Income tax benefit from compensation expense for share-based compensation	373	341	340
Total fair value of shares vested, at vest date	$ 1,591	$ 1,633	$ 1,230
Weighted-average grant-date fair value of shares issued during the period in compensation and benefit plans other than stock options	$ 412.67	$ 355.91	$ 263.89
Performance shares [Member]
Share-Based Compensation and Benefit Plans
Shares awarded or issued under employee benefit plans, shares	4	4	5

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

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-Name Accounting Standards Codification
-Topic 718
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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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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).

+ References

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Number of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

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