Summary of significant accounting policies - Narrative (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Research and Development Expense [Abstract]
Reverse stock split ratio			0.1667
Deferred offering costs	$ 300,000		$ 300,000		$ 0
Restricted cash	100,000	$ 100,000	100,000	$ 100,000	$ 100,000
Change in fair value of warrant liability		5,549,000		5,549,000
Research and development expense	$ 0	$ 0	$ 0	$ 0
Number of operating segments \| segment			1

Research And Development Milestone Expense

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Specific incremental costs directly attributable to a proposed or actual offering of securities which are deferred at the end of the reporting period.

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Amount of expense (income) related to adjustment to fair value of warrant liability.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

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