Aggregate number of common shares reserved for future issuance.

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-Topic 210
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Amount of cost for defined contribution plan.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
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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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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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Percentage of compensation withheld to cover purchase price of common stock

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Purchase price of common stock as percentage of lower of fair market value of common stock share on first day of offering period or last day of purchase period

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Share-based compensation arrangement by share-based payment award, employer contribution as a percentage of employee's annual salary

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Employee Benefits And Stock-Based Compensation (401(k) Plan To 2007 Employee Stock Purchase Plan) (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer contribution as a percentage of employee's annual salary	8.00%
Employer contribution under the plan	$ 4.7	$ 4.3	$ 4.0
Purchase price of common stock as percentage of lower of fair market value of common stock share on first day of offering period or last day of purchase period	85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	3.1
401 (k) Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee's contribution under the plan	50.00%
Two Thousand Six Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock were reserved for issuance	9.0
Minimum [Member] \| Two Thousand Seven Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of compensation withheld to cover purchase price of common stock	2.00%
Maximum [Member] \| Two Thousand Seven Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of compensation withheld to cover purchase price of common stock	25.00%