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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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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

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Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Stock-Based Compensation (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-Based Compensation
Stock-based compensation expense	$ 2,100			$ 2,400			$ 6,100	$ 5,600
Proceeds from exercise of stock options							$ 3,039	$ 1,289
Common Stock
Stock-Based Compensation
Exercise of stock options (in shares)	97,000	104,000	288,000	66,000	46,000	75,000
Common Stock \| Employee stock purchase plan
Stock-Based Compensation
Exercise of stock options (in shares)	100,000						700,000	300,000
Proceeds from exercise of stock options	$ 600			$ 500			$ 3,400	$ 1,700
2000 Stock Plan
Stock-Based Compensation
Number of shares of common stock available for future grant	0						0