Shareholders’ equity (Details) - shares	Sep. 15, 2017	Mar. 31, 2018	Dec. 31, 2017
Shareholders’ equity
Shares authorized	5,000,000	60,000,000	60,000,000
Commission fee based on gross proceeds of shares sold	3.00%

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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