Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Number of Shares, Outstanding Beginning of Period			413,858
Number of options granted			0
Number of Shares, Exercised			(38,183)
Number of Shares, Canceled			0
Number of Shares, Outstanding Ending of Period	375,675		375,675
Number of Shares, Exercisable	338,475		338,475
Number of Shares, Vested and expected to vest	367,885		367,885
Weighted-Average Exercise Price, Outstanding Beginning of Period			$ 31.09
Weighted-Average Exercise Price, Granted			0.00
Weighted-Average Exercise Price, Exercised			29.03
Weighted-Average Exercise Price, Canceled			0.00
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 31.30		31.30
Weighted-Average Exercise Price, Exercisable	27.33		27.33
Weighted-Average Exercise Price, Vested and expected to vest	$ 30.53		$ 30.53
Weighted-Average Remaining Contractual Term, Outstanding (in years)			3 years 4 months 2 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)			2 years 10 months 17 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)			3 years 3 months
Aggregate Intrinsic Value, Outstanding	$ 15,997,701		$ 15,997,701
Aggregate Intrinsic Value, Exercisable	15,754,785		15,754,785
Aggregate Intrinsic Value, Vested and expected to vest	15,946,834		15,946,834
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value			2,100,000	$ 5,100,000
Allocated Share-based Compensation Expense	4,563,000	$ 3,699,000	$ 13,740,000	$ 9,947,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate			14.07%	12.58%
Employee Stock Option [Member]
Allocated Share-based Compensation Expense	$ 40,000	$ 100,000	$ 100,000	$ 300,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			2 years 7 months 6 days

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

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

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 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 options outstanding. 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 fully vested and expected to vest options outstanding that can be converted into shares under option plan. 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 exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. 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 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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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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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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents 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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