Stock-Based Compensation - Options Outstanding (Details) - $ / shares	9 Months Ended
Sep. 30, 2020
Stock-Based Compensation
Outstanding - Number of Options, Beginning Balance	18,268,372
Exercised - Number of Options	(2,789,473)
Granted - Number of Options	1,245,686
Expired - Number of Options	(110,430)
Forfeited - Number of Options	(658,125)
Outstanding - Number of Options, Ending Balance	15,956,030
Vested and expected to vest - Number of options	15,956,030
Exercisable - Number of Options	9,153,348
Outstanding - Weighted Average Exercise Price, Beginning balance	$ 2.58
Exercised - Weighted Average Exercise Price	1.39
Granted - Weighted Average Exercise Price	2.92
Expired - Weighted Average Exercise Price	4.96
Forfeited - Weighted Average Exercise Price	3.89
Outstanding - Weighted Average Exercise Price, Ending Balance	2.75
Vested and expected to vest - Weighted Average Exercise Price	2.75
Exercisable - Weighted Average Exercise Price	$ 2.35

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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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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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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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 of the plan that expired.

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

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