Property, plant and equipment - Net book value of assets under finance leases (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Net book value of assets under finance leases
Recognised finance lease as assets	$ 12.4	$ 4.7
Computer hardware
Net book value of assets under finance leases
Recognised finance lease as assets	5.2	4.6
Furniture and fixtures
Net book value of assets under finance leases
Recognised finance lease as assets	$ 7.2	$ 0.1

The amount of assets recognised by the entity, which are leased under finance leases.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2019-01-01
-Name IAS
-Number 17
-IssueDate 2017-01-01
-Paragraph 31
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=17&date=2017-03-02&anchor=para_31_a&doctype=Standard&book=B
-URIDate 2017-03-09

Name:	ifrs-full_RecognisedFinanceLeaseAsAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant