Stock-based compensation - Narratives (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended
Jan. 01, 2025	Sep. 30, 2025
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation expense not yet recognized, recognition period (in years)		1 year 10 months 24 days
Share based compensation expense not yet recognized other than options		$ 5.9
Granted (in usd per share)		$ 3.19
Granted (in shares)		1,667,362
2021 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Additional shares authorized for issuance (in shares)	5,768,113
Shares available for grant (in shares)		5,483,484
2023 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award
Shares available for employee (in shares)		1,724,200
2020 Plan \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation expense not yet recognized, options		$ 22.0
Share based compensation expense not yet recognized, recognition period (in years)		2 years 1 month 6 days

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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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Amount of cost to be recognized for option under share-based payment arrangement.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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

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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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