Deferred Consideration - Summary of valuation of deferred consideration (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Disclosure Of Valuation Of Deferred Consideration [Line Item]
Discount rate	9.00%	9.00%
Perpetual growth rate	1.70%	0.90%
Minimum [Member]
Disclosure Of Valuation Of Deferred Consideration [Line Item]
Forward-looking gold price	$ 1,717	$ 1,903
Maximum [Member]
Disclosure Of Valuation Of Deferred Consideration [Line Item]
Forward-looking gold price	3,201	2,662
Weighted Average [Member]
Disclosure Of Valuation Of Deferred Consideration [Line Item]
Forward-looking gold price	$ 2,136	$ 2,117