Stock Award Plans, Director Plan Stock Option Activity (Details) - Director Plan [Member]	12 Months Ended
Dec. 31, 2020 $ / shares shares
Stock Award Plan Information [Abstract]
Shares available for future grants (in shares)	421,220
Stock Options [Member]
Stock Award Plan Information [Abstract]
Term of grant	10 years
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period Start (in shares)	115,756
Exercised (in shares)	(12,000)
Outstanding at Period End (in shares)	103,756
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start (in dollars per share) \| $ / shares	$ 73.68
Exercised (in dollars per share) \| $ / shares	41.24
Outstanding at Period End (in dollars per share) \| $ / shares	$ 77.44
Restricted Stock [Member]
Stock Award Plan Information [Abstract]
Vesting period	6 months

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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

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