Related party disclosures - Summary of Total Compensation of Key Management Personnel (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation of key management personnel [abstract]
Short-term employment benefits	$ 15.8	$ 18.2	$ 21.3
Contributions to defined contribution pension plans	0.5	0.5	0.6
Equity compensation benefits	12.1	13.0	10.2
Termination benefits			1.9
Total compensation of key management personnel	$ 28.4	$ 31.7	$ 34.0

The amount of compensation to key management personnel. [Refer: Key management personnel of entity or parent [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-IssueDate 2019-01-01
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The amount of compensation to key management personnel in the form of post-employment benefits. [Refer: Key management personnel of entity or parent [member]]

+ References

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The amount of compensation to key management personnel in the form of share-based payments. [Refer: Key management personnel of entity or parent [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The amount of compensation to key management personnel in the form of short-term employee benefits. [Refer: Key management personnel of entity or parent [member]]

+ References

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- Definition

The amount of compensation to key management personnel in the form of termination benefits. [Refer: Termination benefits expense; Key management personnel of entity or parent [member]]

+ References

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Compensation of key management personnel abstract.

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