Revenue recognition (Details)	9 Months Ended
Sep. 30, 2019 customer
Revenue recognition
Minimum number of customers	200
Minimum
Revenue recognition
Period of payment	30 days
Maximum
Revenue recognition
Period of payment	45 days

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration