Share-based compensation - Unrecognized Compensation Cost and Period Of Recognition (Details) $ in Millions	6 Months Ended
Jun. 30, 2020 USD ($)
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 8.0
Weighted average recognition period (years)	1 year 5 months 24 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 1.6
Weighted average recognition period (years)	1 year 8 months 12 days
IPO incentive awards \| Performance share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 2.1
Weighted average recognition period (years)	1 year 6 months
Long term incentive plan 2019 \| Performance share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 1.0
Weighted average recognition period (years)	1 year 6 months
2018 Long Term Incentive Plan (LTIP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 0.2
Weighted average recognition period (years)	6 months

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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