Summary of significant accounting policies - Narrative (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)
Research and Development Expense [Abstract]
Reverse stock split ratio	0.1667
Cash equivalents	$ 0	$ 0
Restricted cash	100	100
Impairment losses	0	0
Deferred Offering Costs	0
Accretion	0	0
Change in fair value of warrant liability	5,538
Research and development expense	$ 0	$ 0
Number of operating segments \| segment	1
Expected dividend yield	0.00%

Research And Development Milestone Expense

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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- Definition

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

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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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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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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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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Value of accretion of temporary equity to its redemption value during the period.

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