Finance lease obligations (Narrative) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Statement [Line Items]
Proceeds from sale and leaseback transactions	$ 67,275
Finance lease obligations [Member] \| Bottom of range [Member]
Statement [Line Items]
Borrowings, interest rate	1.95%
Finance lease obligations [Member] \| Top of range [Member]
Statement [Line Items]
Borrowings, interest rate	4.45%

The interest rate on borrowings. [Refer: Borrowings]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 7
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_7&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_BorrowingsInterestRate
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant