Retirement plans - Actuarial assumptions and sensitivity analysis (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rates	3.90%	3.70%
Discount rate
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible decrease in actuarial assumption	1.00%
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption	$ 5.4

The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 144
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_144&doctype=Standard
-URIDate 2017-03-09

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- Definition

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.

+ References

No definition available.

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 145
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_145_a&doctype=Standard
-URIDate 2017-03-09

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- Definition

The reasonably possible percentage of the decrease in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]]

+ References

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