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Percentage of annual increase in reserves on total number of ordinary shares outstanding.

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No definition available.

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Period for vesting equity-based award in equal monthly installment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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Aggregate number of common shares reserved for future issuance.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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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- Definition

Percentage of vesting of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Share-based compensation (Details)	1 Months Ended	12 Months Ended
Share-based compensation (Details)	May 31, 2019 shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares	Dec. 31, 2017	Jan. 01, 2020 shares	May 27, 2019 £ / shares
Stock option
Share-based compensation.
Exercise price \| $ / shares		$ 9.57	$ 1.01
Employee Share Purchase Plan
Share-based compensation.
Number of ordinary shares reserved for issuance	215,000
Percentage of ordinary shares at a price per share equal to the fair market value on offering date or purchase date	85.00%
2017 Plan
Share-based compensation.
Number of shares reserved for issuance					719,748
2019 Plan
Share-based compensation.
Number of ordinary shares reserved for issuance	2,470,583
2019 Plan \| Stock option
Share-based compensation.
Percentage of annual increase in reserves on total number of ordinary shares outstanding	4.00%
Number of shares available for issuance		872,646
Contractual life	10 years
2019 Plan \| Stock option \| First anniversary
Share-based compensation.
Vesting Percentage	25.00%
2019 Plan \| Stock option \| 36 equal monthly installments
Share-based compensation.
Number of equal monthly installments for vesting remaining awards	36 months
2019 Plan \| Minimum \| Stock option
Share-based compensation.
Vesting period	3 years
2019 Plan \| Maximum \| Stock option
Share-based compensation.
Vesting period	4 years
Pre-IPO Share Options and restricted shares \| Stock option
Share-based compensation.
Contractual life		10 years
Vesting period		4 years
Pre-IPO Share Options and restricted shares \| Stock option \| First anniversary
Share-based compensation.
Vesting Percentage		25.00%
Pre-IPO Share Options and restricted shares \| Stock option \| 36 equal monthly installments
Share-based compensation.
Number of equal monthly installments for vesting remaining awards		36 months
Pre-IPO Share Options and restricted shares \| Stock option \| United Kingdom
Share-based compensation.
Exercise price \| £ / shares						£ 0.01
Pre-IPO Share Options and restricted shares \| Performance based option \| First anniversary
Share-based compensation.
Vesting Percentage			20.00%	20.00%
Pre-IPO Share Options and restricted shares \| Performance based option \| 36 equal monthly installments
Share-based compensation.
Vesting Percentage			60.00%	60.00%
Number of equal monthly installments for vesting remaining awards			36 months	36 months
Pre-IPO Share Options and restricted shares \| Performance based option \| Earlier of the fourth anniversary
Share-based compensation.
Vesting Percentage			20.00%	20.00%