Significant accounting policies - Other (Details)	3 Months Ended
Mar. 31, 2018 USD ($) item	Jan. 02, 2018 USD ($)
Significant accounting policies
Ifrs Cumulative Effect Of New Accounting Principle In Period Of Adoption		$ 27,100,000
Number of equity investments accounted for at cost \| item	1
Carrying value	$ 4,000,000
Number of loan receivable carried at amortized cost \| item	1
Loan receivable at amortized cost	$ 30,100,000
Impairment loss recognized	$ 0

The amount of impairment loss recognised in profit or loss. [Refer: Impairment loss; Profit (loss)]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2017-01-01
-Paragraph 126
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_126_a&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2017-01-01
-Paragraph 129
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_129_a&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_ImpairmentLossRecognisedInProfitOrLoss
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration