Summary of significant accounting policies (Details) $ in Millions	Sep. 30, 2018 USD ($)
ASU 2014-09
Summary of significant accounting policies
Cumulative effect adjustment to retained earnings	$ 1.6

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

No definition available.

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