Summary of significant accounting policies - Stock split (Details)	1 Months Ended
Sep. 30, 2019
Common Stock
Deferred offering costs
Stock split ratio	0.62325
Preferred Stock
Deferred offering costs
Stock split ratio	0.62325

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB TOPIC 4.C)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770

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