Summary of significant accounting policies (Details 4) - shares	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Previously reported
Shares issued	5,322,459	3,260,559	3,260,559	2,229,609
Restatement
Shares issued	7,899,832	7,899,832	7,899,832	7,899,832

Number of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=126973232&loc=d3e21463-112644

Name:	us-gaap_SharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant