Income taxes - Unrecognized deferred tax assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Unrecognized deferred tax assets
Unrecognized deferred tax assets	$ 268.0	$ 392.4
Tax loss carry forwards
Unrecognized deferred tax assets
Unrecognized deferred tax assets	177.6	254.1
Other items
Unrecognized deferred tax assets
Unrecognized deferred tax assets	$ 90.4	$ 138.3

The amount of deductible temporary differences for which no deferred tax asset is recognised in the statement of financial position. [Refer: Temporary differences [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2017-01-01
-Paragraph 81
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_e&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_DeductibleTemporaryDifferencesForWhichNoDeferredTaxAssetIsRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant