Commitments and contingencies - Legal proceedings (Details) - Suit for damages $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($) location
Commitments and contingencies
Number of venues under suit \| location	1
Paid loss \| $	$ 1,100

Amount of loss contingency liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant