Deferred Consideration - Schedule of Deferred Consideration (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Contractual gold payments	$ 4,270	$ 3,760
Contractual gold payments – gold ounces paid	2,375	2,375
Gain/(loss) on revaluation of deferred consideration - gold payments	$ 2,832	$ (2,208)