Share-based payments (Narrative) (Details)	3 Months Ended
Mar. 31, 2021 USD ($) D	Dec. 31, 2020 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of trading days of volume weighted average price for fair value estimation \| D	20
Maximum employee contribution, percentage	4.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer matching contribution, percentage	50.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer matching contribution, percentage	100.00%
Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 11,000,000
Unrecognized compensation costs, period for recognition	2 years 8 months 12 days
Performance Share Unit Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market value of shares vested and released	$ 0	$ 0
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 15,976,000
Unrecognized compensation costs, period for recognition	2 years 3 months 18 days
Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 2,818,000
Unrecognized compensation costs, period for recognition	1 year 9 months 18 days
Number of trading days of volume weighted average price for fair value estimation \| D	20
Deferred Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 0
Share unit liability	$ 7,900,000	$ 9,597,000

Employee Stock Purchase Plan, Employer Matching Contribution, Percent of Match

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- Definition

Employee Stock Purchase Plan, Maximum Annual Contributions Per Employee, Percent

+ References

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- Definition

The number of specified trading days for weighted average price of the Company's common shares listed on the New York Stock Exchange to estimate the fair values on grant date and at each reporting date.

+ References

No definition available.

+ Details

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. Additionally, share-based awards which were paid or settled.

+ References

No definition available.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

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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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.

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- Definition

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

+ References

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- Definition

Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

+ References

No definition available.

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