Share Based Compensation - Outstanding and exercisable options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Outstanding and exercisable options, weighted average exercise price
Weighted average remaining contractual life (in years)	8 years 1 month 6 days	8 years 4 months 24 days
Weighted average remaining contractual life for vested options (in years)	7 years	7 years 1 month 6 days
Share-based compensation expense	$ 2,114	$ 1,368
Unrecognized compensation cost	$ 20,601	$ 20,573
Expected period for recognition	2 years 9 months 18 days	3 years 1 month 6 days
Option Plans 2011 and 2019
Outstanding and exercisable options, number of shares
Outstanding at end of period	7,097,189	5,632,224
Exercisable at end of period	3,546,820	2,205,114
Outstanding and exercisable options, weighted average exercise price
Outstanding at end of period	$ 6.64	$ 6.99
Exercisable at end of period	$ 5.83	$ 4.86
2011 Plan
Outstanding and exercisable options, number of shares
Outstanding at beginning of period	1,995,971	2,080,087
Exercised	(9,500)	(16,753)
Cancelled	(19,387)
Outstanding at end of period	1,967,084	2,063,334
Exercisable at end of period	1,825,299	1,613,229
Outstanding and exercisable options, weighted average exercise price
Outstanding at beginning of period	$ 2.07	$ 2.15
Exercised	1.12	0.88
Forfeited	9.42
Cancelled	9.42
Outstanding at end of period	2.00	2.16
Exercisable at end of period	$ 1.95	$ 2.05
2019 Plan
Outstanding and exercisable options, number of shares
Outstanding at beginning of period	3,759,834	1,706,190
Granted	1,385,700	1,863,950
Exercised	(10,267)	(1,250)
Cancelled	(5,162)
Outstanding at end of period	5,130,105	3,568,890
Exercisable at end of period	1,721,521	591,885
Outstanding and exercisable options, weighted average exercise price
Outstanding at beginning of period	$ 9.51	$ 13.55
Granted	5.47	6.31
Exercised	3.76	3.74
Forfeited	8.64
Cancelled	21.48
Outstanding at end of period	8.42	9.77
Exercisable at end of period	9.94	12.55
Weighted average fair values of options granted	$ 4.13	$ 4.79

The number of shares under options that were cancelled during the reporting period pertaining to the stock option plan.

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Weighted average grant-date fair value of options cancelled.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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

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