Major Group Investments Direct and Indirect - Summary of Share Held in Investments in Associates Joint Ventures other Equity Investments and Percentage of Beneficial Interest (Detail) - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Far Southeast Gold Resources Incorporated [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Group beneficial interest	40.00%	40.00%	40.00%
Equity investments [member] \| Asanko Gold Inc [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	22,354,657	0
Group beneficial interest	9.90%	0.00%
Equity investments [member] \| Bezant Resources PLC [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	17,945,922	17,945,922
Group beneficial interest	1.80%	2.90%
Equity investments [member] \| Cardinal Resources Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	42,818,182	42,818,182
Group beneficial interest	11.30%	11.50%
Equity investments [member] \| Cardinal Resources Limited Options [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	38,220,051	38,220,051
Group beneficial interest	25.80%	33.00%
Equity investments [member] \| Cascadero Copper Corporation [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	0	2,025,000
Group beneficial interest	0.00%	1.10%
Equity investments [member] \| Clancy Exploration Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	17,764,783	17,764,783
Group beneficial interest	0.50%	0.60%
Equity investments [member] \| Consolidated Woodjam Copper Corporation [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	16,115,740	12,848,016
Group beneficial interest	19.90%	17.20%
Equity investments [member] \| Fjordland Exploration Incorporated [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	0	363,636
Group beneficial interest	0.00%	0.80%
Equity investments [member] \| Gold Road Resources Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	87,117,909	87,117,909
Group beneficial interest	9.90%	9.90%
Equity investments [member] \| Hummingbird Resources Plc [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	21,258,503	21,258,503
Group beneficial interest	6.00%	6.20%
Equity investments [member] \| Lefroy Exploration Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	14,764,535	0
Group beneficial interest	18.20%	0.00%
Equity investments [member] \| Magmatic Resources Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	17,600,000	0
Group beneficial interest	15.00%	0.00%
Equity investments [member] \| Orsu Metals Corporation [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	2,613,491	2,613,491
Group beneficial interest	7.20%	7.30%
Equity investments [member] \| Radius Gold Incorporated [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	0	3,625,124
Group beneficial interest	0.00%	4.20%
Equity investments [member] \| Red 5 Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Asanko Gold Inc.	246,875,821	246,875,821
Group beneficial interest	19.90%	19.90%
Associates [member] \| Maverix Metals Incorporated [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Maverix Metals Incorporated ("Maverix")	42,850,000	42,850,000
Group beneficial interest	19.90%	27.90%
Associates [member] \| Rusoro Mining Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Maverix Metals Incorporated ("Maverix")	140,000,001	140,000,001
Group beneficial interest	25.70%	25.70%
Joint ventures [member] \| Far Southeast Gold Resources Incorporated [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Adansi Gold Company Limited	1,737,699	1,737,699
Group beneficial interest	40.00%	40.00%
Joint ventures [member] \| Asanko Gold Ghana Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Adansi Gold Company Limited	450,000,000	0
Group beneficial interest	45.00%	0.00%
Joint ventures [member] \| Adansi Gold Company Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Adansi Gold Company Limited	100,000	0
Group beneficial interest	50.00%	0.00%
Joint ventures [member] \| Shika Group Finance Limited [member]
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]
Adansi Gold Company Limited	10,000	0
Group beneficial interest	50.00%	0.00%