Deferred Consideration - Additional Information (Detail) $ in Thousands	Sep. 30, 2020 USD ($) oz	Dec. 31, 2019 USD ($) oz
Business Acquisition [Line Items]
Deferred consideration	$ 207,748	$ 173,024
Deferred consideration, current	17,202	13,953
Deferred consideration, non-current	$ 190,546	$ 159,071
April 1, 2018 through March 31, 2058 [Member]
Business Acquisition [Line Items]
Fixed payment ounces of gold | oz	9,500	9,500
April 1, 2058 and Thereafter [Member]
Business Acquisition [Line Items]
Fixed payment ounces of gold | oz	6,333	6,333