Share-Based Compensation And Share Repurchase Plans (Schedule Of Stock Options Outstanding And Exercisable) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity And Stock-Based Compensation [Line Items]
Weighted Average Exercise Price of Options Outstanding, Granted	$ 16.12	$ 16.40	$ 15.94
Weighted Average Remaining Years of Contractual Life	2 years 9 months 15 days	2 years 10 months 17 days	3 years 1 month 24 days	2 years 7 months 10 days
Aggregate Intrinsic Value, Beginning balance	$ 1,530,528	$ 3,054,325	$ 3,615,191
Aggregate Intrinsic Value, Exercised	185,175	610,249	702,840
Aggregate Intrinsic Value, Ending balance	$ 136,350	$ 1,530,528	$ 3,054,325	$ 3,615,191
Class A [Member]
Equity And Stock-Based Compensation [Line Items]
Number of Stock Options, Beginning balance	586,469	524,589	535,077
Number of Stock Options, Granted	219,408	126,840	169,762
Number of Stock Options, Exercised	(69,500)	(60,000)	(177,750)
Number of Stock Options, Expired	(25,000)	(4,960)	(2,500)
Number of Stock Options Outstanding, Ending balance	711,377	586,469	524,589	535,077
Weighted Average Exercise Price of Options Outstanding, Beginning price	$ 14.01	$ 12.50	$ 9.84
Weighted Average Exercise Price of Options Outstanding, Granted	16.12	16.40	15.94
Weighted Average Exercise Price of Options Outstanding, Exercised	13.42	6.02	7.85
Weighted Average Exercise Price of Options Outstanding, Expired	13.42	12.08	6.23
Weighted Average Exercise Price of Options Outstanding, Ending price	$ 14.74	$ 14.01	$ 12.50	$ 9.84

Equity And Stock Based Compensation [Line Items]

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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 grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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 of the plan that expired.

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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 fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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

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