Deferred Consideration (Detail) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2019		Dec. 31, 2018
Contractual Gold Payments									$ 13,226		$ 8,512
Contractual Gold Payments – gold ounces paid									9,500		6,835	[1]
(Loss)/gain on revaluation of deferred consideration – gold payments	$ (5,354)	$ (6,306)	$ (4,037)	$ 4,404	$ (5,410)	$ 7,732	$ 9,898	$ 12,220	$ (11,293)	[2]	$ 12,220	[2]

[1] Represents payments during the period April 11, 2018 through December 31, 2018.

[2] (Losses)/gains arise due to increases/(decreases) in the forward-looking price of gold and the magnitude of any gain or loss is highly correlated to the magnitude of the change in the forward-looking price of gold. See Note 5 for a reconciliation of changes in the deferred consideration balances