Summary of significant accounting policies - Concentrations of credit risk and of significant suppliers (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Summary of significant accounting policies
Accounts receivable	$ 0	$ 0

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

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