Share-Based Compensation (Schedule Of Stock Option Activity) (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Options outstanding, January 1	1,004,014	920,346	859,182
Options outstanding, December 31	1,033,838	1,004,014	920,346
Options exercisable, December 31	601,994
Weighted Average Exercise Price, Options outstanding, January 1	$ 74.35	$ 69.24	$ 70.11
Weighted Average Exercise Price, Options outstanding, December 31		$ 74.35	$ 69.24
Weighted Average Exercise Price, Options exercisable, December 31
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	3 years 4 months 20 days
Weighted Average Remaining Contractual Life (Years), Options exercisable, December 31	3 years 29 days
Aggregate Intrinsic Value, Options outstanding, December 31	$ 715,000
2005 Plan [Member]
Options exercised			(6,668)
Weighted Average Exercise Price, Options exercised			$ 72.11
2012 Plan [Member]
Options granted	319,669	685,334	560,000
Options exercised	(512,509)	(501,664)	(462,167)
Options forfeited		(100,002)	(30,001)
Weighted Average Exercise Price, Options granted	$ 90.79	$ 79.08	$ 64.33
Weighted Average Exercise Price, Options exercised	$ 72.98	71.52	65.03
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	(16,669)
Weighted Average Exercise Price, Options forfeited	$ 81.37	$ 73.89	$ 66.73
Two Thousand Nineteen Stock Option Plan [Member]
Options granted	272,331
Weighted Average Exercise Price, Options granted	$ 89.76
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	(32,998)
Weighted Average Exercise Price, Options forfeited	$ 90.79
Grant Date 2-22-2016
Options outstanding, December 31	20,000
Weighted Average Exercise Price, Options outstanding, December 31	$ 60.52
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	1 month 24 days
Grant Date 2-22-2017
Options outstanding, December 31	55,331
Weighted Average Exercise Price, Options outstanding, December 31	$ 74.78
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	1 year 1 month 24 days
Grant Date 2-20-2018 [Member]
Options outstanding, December 31	88,170
Weighted Average Exercise Price, Options outstanding, December 31	$ 64.33
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	2 years 1 month 20 days
Grant Date 2-21-2019 [Member]
Options outstanding, December 31	313,504
Weighted Average Exercise Price, Options outstanding, December 31	$ 79.96
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	3 years 1 month 20 days
Grant Date 2-21-2020
Options outstanding, December 31	549,333
Weighted Average Exercise Price, Options outstanding, December 31	$ 90.79
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	4 years 1 month 24 days
Grant Date 5-1-2020
Options outstanding, December 31	7,500
Weighted Average Exercise Price, Options outstanding, December 31	$ 53.76
Weighted Average Remaining Contractual Life (Years), Options outstanding, December 31	4 years 3 months 29 days

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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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.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

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

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