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Share-based compensation - Weighted average assumptions (Details) - SARs and TSARs	12 Months Ended
	Dec. 31, 2020 USD ($) year	Dec. 31, 2019 USD ($) year
Disclosure of terms and conditions of share-based payment arrangement [line items]
Risk-free interest rate	0.10%	1.60%
Expected dividend yield	0.30%	3.70%
Expected life of SARs and TSARs (years) | year	1.6	1.2
Expected volatility	60.00%	38.00%
Expected forfeitures	0.00%	0.10%
Weighted average fair value (USD per share) | $	$ 13.36	$ 3.03

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

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The weighted average fair value at the measurement date of granted equity instruments other than share options. [Refer: Weighted average [member]]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 47
-Subparagraph b
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-URIDate 2020-01-01

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