STOCKHOLDERS' EQUITY - Compensation Plan (Details) $ / shares in Units, $ in Millions		1 Months Ended				12 Months Ended
	Feb. 21, 2019 USD ($) $ / shares	Nov. 30, 2018 $ / shares	Nov. 30, 2018 $ / shares	Jan. 31, 2015 $ / shares	Jan. 31, 2015 $ / shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Grupo Mexico and Americas Mining
Retained earnings
Dividends paid as cash dividend (in dollars per share) | $ / shares	$ 0.44428
Settlement dividend paid | $	$ 36.5
Legal fees paid | $	$ 13.5
Peruvian Operations
Non-controlling interest
Investment shareholders' interest in Peruvian Branch (as a percent)						0.71%
Employee Stock Purchase 2015 Plan
Information related to compensation cost
Purchase price for initial subscription (in dollars per share) | (per share)				$ 1.86	$ 38.44	$ 1.86
Percentage of title acquired by employee in every two years on shares paid in previous two years						50.00%
Period of plan						8 years
Ratio of bonus shares granted to participant						0.1
Stock based compensation expense | $						$ 0.6	$ 0.6	$ 0.6
Unrecognized compensation expense | $						$ 0.8	$ 1.4	$ 2.0
Stock award activity, Shares
Outstanding shares at the beginning of the period | shares						1,264,410	1,379,734
Exercised (in shares) | shares						(397,176)	(115,324)
Outstanding shares at the end of the period | shares						867,234	1,264,410	1,379,734
Unit Weighted Average Grant Date Fair Value
Outstanding shares at the beginning of the period (in dollars per share) | $ / shares						$ 2.63	$ 2.63
Exercised (in dollars per share) | $ / shares						2.63	2.63
Outstanding shares at the end of the period (in dollars per share) | $ / shares						$ 2.63	$ 2.63	$ 2.63
Employee Stock Purchase 2018 Plan
Information related to compensation cost
Purchase price for initial subscription (in dollars per share) | (per share)		$ 1.86	$ 37.89
Percentage of title acquired by employee in every two years on shares paid in previous two years						50.00%
Period of plan						8 years
Ratio of bonus shares granted to participant						0.1
Stock based compensation expense | $						$ 0.7	$ 0.7	$ 0.7
Unrecognized compensation expense | $						$ 3.1	$ 3.8	$ 4.5
Stock award activity, Shares
Outstanding shares at the beginning of the period | shares						3,918,458	4,002,898
Exercised (in shares) | shares						(744,534)	(84,440)
Outstanding shares at the end of the period | shares						3,173,924	3,918,458	4,002,898
Unit Weighted Average Grant Date Fair Value
Outstanding shares at the beginning of the period (in dollars per share) | $ / shares						$ 1.86	$ 1.86
Exercised (in dollars per share) | $ / shares						1.86	1.86
Outstanding shares at the end of the period (in dollars per share) | $ / shares						$ 1.86	$ 1.86	$ 1.86
Directors' Stock Award Plan
Information related to compensation cost
Stock based compensation expense | $						$ 0.3	$ 0.4
Stock award activity, Shares
Granted (in shares) | shares						13,600	14,400