Stock-Based Compensation (Schedule of Share Option Activity) (Details) - Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Options Outstanding
Options outstanding	100,279	41,581
Granted	511,800	77,514
Cancelled/forfeited	(9,396)	(18,816)
Options outstanding	602,683	100,279	41,581
Unvested	525,010
Vested and exercisable	77,673
Weighted Average Exercise Price Per Share
Options outstanding	$ 54.40	$ 133.60
Granted	4.17	14.20
Cancelled/forfeited (in dollars per share)	101.05	64.60
Options outstanding	11.01	$ 54.40	$ 133.60
Unvested	4.64
Vested and exercisable	$ 54.05
Weighted Average Remaining Contractual Term (Years)
Options outstanding	9 years 4 months 21 days	8 years 7 months 13 days	8 years 1 month 17 days
Unvested	9 years 9 months 18 days
Vested and exercisable	6 years 7 months 10 days
Aggregate Intrinsic Value
Options outstanding	$ 1,861	$ 4
Unvested	1,829
Vested and exercisable	$ 32

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Represents the amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options unvested.

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Weighted average remaining contractual term for unvested options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Gross number of share options (or share units) granted during the period.

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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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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. 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 exercisable options that may 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 exercisable or convertible options. 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 per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of non-vested options outstanding.

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Weighted average grant-date fair value of non-vested options outstanding.

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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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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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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