Stockholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2020
Number of Stock Options
Outstanding (in shares)	3,680,146
Exercised (in shares)	(506,105)
Forfeited or expired (in shares)	(85,000)
Outstanding (in shares)	3,089,041
Exercisable (in shares)	3,053,207
Weighted- average Exercise Price
Outstanding (in dollars per share)	$ 3.60
Exercised (in dollars per share)	3.98
Forfeited or expired (in dollars per share)	3.65
Outstanding (in dollars per share)	3.54
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 3.55
Outstanding, Weighted-Average Remaining Contractual Life	4 years 4 months 24 days
Exercisable, Weighted-Average Remaining Contractual Life	4 years 4 months 24 days
Outstanding, Aggregate Intrinsic Value	$ 8,257
Exercisable, Aggregate Intrinsic Value	$ 8,125

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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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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

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