Goodwill - Summary of Key Assumptions Used for Assessing the Recoverable Amount of Goodwil (Detail) - Goodwill [member]	12 Months Ended
Dec. 31, 2017 $ / oz
Disclosure Of Cash Flow Statement [Line Items]
Gold price	1,300
Discount rate	7.00%
Bottom of range [member]
Disclosure Of Cash Flow Statement [Line Items]
Silver price	16
Top of range [member]
Disclosure Of Cash Flow Statement [Line Items]
Silver price	18

The discount rate used in the current measurement of fair value less costs of disposal.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2017-01-01
-Paragraph 130
-Subparagraph f
-Clause iii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_130_f_iii&doctype=Standard
-URIDate 2017-03-09

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