Stock-based compensation - Stock-based compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Stock-based compensation expense	$ 5,565	$ 867	$ 770
Number of outstanding options modified		2,000
Exercise price of the stock options		$ 34.12	$ 1.17
Unrecognized compensation cost related to the unvested stock-based awards	$ 9,300	$ 2,200
Weighted average periods over which expense is expected to be recognized	1 year 9 months 18 days	1 year 8 months 12 days
Research and Development Expense
Stock-based compensation
Stock-based compensation expense	$ 1,981	$ 399	$ 295
General and Administrative Expense
Stock-based compensation
Stock-based compensation expense	$ 3,584	$ 468	$ 475

Represents the number of outstanding options modified to increase the exercise price.

No definition available.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

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

+ References

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- Definition

Amount of noncash expense for share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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- Definition

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.

+ References

No definition available.

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- Definition

Weighted average price at which grantees could acquire or could have acquired the underlying shares with respect to any other type of change in shares reserved for issuance.

+ References

No definition available.

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