Convertible preferred stock and stockholders’ equity - Common stock (Details) - shares shares in Thousands	Dec. 31, 2019	Dec. 31, 2018
Common stock reserved for issuance	5,830	4,154
Stock options
Common stock reserved for issuance	4,798	3,959
Restricted stock awards
Common stock reserved for issuance	1,032	195

Aggregate number of common shares reserved for future issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant