Stock Options And Employee Stock Purchase Plan (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Number of options outstanding	476,811		518,341
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate	11.57%	12.63%
Share-based Payment Arrangement, Expense	$ 6,313	$ 5,086
Share-based Payment Arrangement, Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 6,600		$ 6,800
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	5 years 8 months 12 days
Share-based Payment Arrangement, Expense	$ 200	$ 200
Restricted (Performance) Stock [Member]
Shares, Granted	82,112	72,734
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	0.71%	2.53%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	27.00%	28.30%
Restricted Stock [Member]
Number of stocks outstanding	927,938		1,105,059
Shares, Granted	1,268
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	4 years 7 months 6 days
Restricted Stock Units (RSUs) [Member]
Number of stocks outstanding	194,527		20,874
Shares, Granted	179,361
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	5 years 7 months 6 days
2007 Stock Plan [Member]
Maximum issuance of common stock	4,500,000
Number of options outstanding	53,811
Number of stocks outstanding	340
2015 Stock Option Plan [Member]
Maximum issuance of common stock	4,200,000
Number of options outstanding	423,000
Number of stocks outstanding	194,187
2001 Employee Stock Purchase Plan [Member] \| Common Stock [Member]
Market value of common stock on the date of grant for incentive stock options	85.00%
Maximum earnings withheld by the employees	15.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate	5.80%	1.96%
Number of shares purchased under the plan	0	0
Cash received upon the issuance of common stock	$ 0	$ 0
Number of shares available for issuance	1,523,568
Share-based Payment Arrangement, Expense	$ 500	$ 400
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	1.57%	2.32%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term	6 months	6 months
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	1.19%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	23.95%	22.17%
Minimum [Member]
Market value of common stock on the date of grant for incentive stock options	85.00%

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate

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

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The cash inflow associated with the amount received from the stock plan during the period.

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Discount rate from fair value on offering date that participants pay for shares.

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The number of grants made 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).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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Number of shares authorized for issuance under share-based payment arrangement.

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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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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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