Stock Options and Incentive Plans (Schedules of Stock Option Activity) (Details) - Stock Options [Member] - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares
Shares under option January 1	18,940	29,340	62,390
Options canceled			150
Options exercised	6,990	10,400	32,900
Shares under option at December 31	11,950	18,940	29,340
Options exercisable at December 31	11,950	18,940	29,340
Weighted Average Exercise Price
Shares under option January 1	$ 17.87	$ 18.40	$ 18.28
Options canceled			20.63
Options exercised	16.06	19.38	18.16
Shares under option December 31	18.93	17.87	18.40
Options exercisable December 31	$ 18.93	$ 17.87	$ 18.40

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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