Share-based compensation - Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022
Number of shares
Options, Beginning balance	2,519,405
Options, Granted	658,900
Options, Forfeited	(98,216)
Options, Expired	(55,670)
Options, Ending balance	3,024,419
Options, Exercisable	1,669,562
Weighted Average Exercise price
Beginning price	$ 9.60
Granted	4.87
Forfeited	11.56
Expired	16.59
Ending price	8.38
Exercisable	8.76
Weighted average grant date fair value	$ 3.67	$ 2.65
Intrinsic value, exercisable	$ 6.7
Intrinsic value, outstanding	11.2
Intrinsic value, exercised	$ 0.1

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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

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.