Net income per common share - Basic and diluted (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Earnings per share [abstract]
Basic net income per common share (in usd per share)	$ 7.07	$ 3.64
Diluted net income per common share (in usd per share)	$ 6.92	$ 3.64

The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator), divided by the weighted average number of ordinary shares outstanding during the period (the denominator), both adjusted for the effects of all dilutive potential ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2017-01-01
-Paragraph 66
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=33&date=2017-03-01&anchor=para_66&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_DilutedEarningsLossPerShare
Namespace Prefix:	ifrs-full_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration