Share-based compensation - Unrecognized Compensation Cost and Period Of Recognition (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($)
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 9.8
Weighted average recognition period (years)	1 year 7 months 30 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 1.8
Weighted average recognition period (years)	1 year 11 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	$ 2.6
Weighted average recognition period (years)	1 year 9 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	$ 1.1
Weighted average recognition period (years)	1 year 9 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)	9 months

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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=109197908&loc=d3e5070-113901

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

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