Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Beginning stock options outstanding (in shares)	1,464,766	1,664,781	1,911,121
Granted (in shares)			374,215
Exercised (in shares)	0	(7,021)	(488,303)
Forfeited (in shares)	(542,151)	(192,994)	(132,252)
Ending stock options outstanding (in shares)	922,615	1,464,766	1,664,781
Weighted Average Exercise Price Per Share
Beginning stock options outstanding (in dollars per share)	$ 7.41	$ 8.31	$ 7.79
Granted (in dollars per share)			7.49
Exercised (in dollars per share)		4.94	5.76
Forfeited (in dollars per share)	7.94	15.26	7.89
Ending stock options outstanding (in dollars per share)	$ 7.10	$ 7.41	$ 8.31
Vested and expected to vest at December 31, 2020
Number of Shares	922,246
Weighted Average Exercise Price Per Share (in dollars per share)	$ 7.10
Weighted Average Contractual Life	5 years 3 months 14 days
Aggregate Intrinsic Value	$ 35
December 31, 2020
Number of Shares	888,350
Weighted Average Exercise Price Per Share (in dollars per share)	$ 7.08
Weighted Average Contractual Life	5 years 2 months 15 days
Aggregate Intrinsic Value	$ 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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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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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 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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