Revenue and segmented information - Revenue based on geographic location (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Geographical areas disclosures
Revenues	$ 1,631.2	$ 1,557.5
United States
Geographical areas disclosures
Revenues	743.8	447.2
Canada
Geographical areas disclosures
Revenues	329.9	424.4
Asia
Geographical areas disclosures
Revenues	295.3	311.9
Europe
Geographical areas disclosures
Revenues	207.1	284.5
Australia
Geographical areas disclosures
Revenues	29.6	29.7
South America
Geographical areas disclosures
Revenues	16.7	58.1
Other
Geographical areas disclosures
Revenues	$ 8.8	$ 1.7

The income arising in the course of an entity's ordinary activities. Income is increases in economic benefits during the accounting period in the form of inflows or enhancements of assets or decreases of liabilities that result in an increase in equity, other than those relating to contributions from equity participants.

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+ Details