Revenue and segmented information - Additional information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Revenue and segmented information
Orbital income	$ 34.8	$ 30.9
Aggregate amount of revenue recognized to date less loss recognized to date for construction contracts in progress	2,770.5	2,707.6
Advance payments received for construction contracts in progress	238.8	266.6
Retentions in connection with construction contracts	$ 6.9	$ 7.0

The amount of advances received by the entity before the related work is performed on construction contracts.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRIC
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-IssueDate 2017-01-01
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate amount of costs incurred and recognised profits, less recognised losses, to date on construction contracts in progress.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IAS
-Number 11
-IssueDate 2017-01-01
-Paragraph 40
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=11&date=2017-03-02&anchor=para_40_a&doctype=Standard&book=B
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRIC
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-IssueDate 2017-01-01
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-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRIC&num=15&date=2017-03-02&anchor=para_21_a&doctype=Standard&book=B
-URIDate 2017-03-09

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- Definition

The amount of progress billings on construction contracts that are not paid until the conditions specified in the contract for the payment of such amounts have been satisfied or until defects have been rectified. [Refer: Progress billings]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IAS
-Number 11
-IssueDate 2017-01-01
-Paragraph 40
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- Definition

+ References

No definition available.

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- Definition

The orbital income arising in the course of an entity's ordinary activities.

+ References

No definition available.

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