| Weighted average share price, share options granted | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Concept not required as a result of 2018 annual improvements | en | http://www.xbrl.org/2009/role/deprecatedLabel | http://www.xbrl.org/2003/role/link |
| 2019-01-01 | en | http://www.xbrl.org/2009/role/deprecatedDateLabel | http://www.xbrl.org/2003/role/link |
| The weighted average share price used as input to the option pricing model to calculate the fair value of share options granted. [Refer: Option pricing model [member]; Weighted average [member]] | en | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |