Share-based payment plans - Intrinsic value (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Cash settled
Share-based payment plans
Intrinsic value of cash-settled share based payment award	$ 2.3	$ 2.3

The intrinsic value of liabilities arising from share-based transactions for which the counterparty's right to cash or other assets had vested by the end of the period (for example, vested share appreciation rights). The intrinsic value is the difference between the fair value of the shares to which the counterparty has the (conditional or unconditional) right to subscribe, or which it has the right to receive, and the price (if any) that the counterparty is (or will be) required to pay for those shares. Share-based payment transactions are transactions in which the entity: (a) receives goods or services from the supplier of those goods or services (including an employee) in a share-based payment arrangement; or (b) incurs an obligation to settle the transaction with the supplier in a share-based payment arrangement when another group entity receives those goods or services, for which the counterparty's right to cash or other assets had vested by the end of the period (for example, vested share appreciation rights).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2017-01-01
-Paragraph 51
-Subparagraph b
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_51_b_ii&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_IntrinsicValueOfLiabilitiesFromSharebasedPaymentTransactionsForWhichCounterpartysRightToCashOrOtherAssetsVested2011
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant