ASSET RETIREMENT AND ENVIRONMENTAL RECLAMATION OBLIGATIONS - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) pit	Dec. 31, 2023 USD ($)
Asset Retirement Obligation And Accrual For Environmental Loss Contingencies [Line Items]
Environmental Loss Contingency, Statement Of Financial Position, Extensible Enumeration, Not Disclosed Flag	environmental remediation liability
Colowyo Mine Pit - Final Reclamation
Asset Retirement Obligation And Accrual For Environmental Loss Contingencies [Line Items]
Number of mine pits in final reclamation | pit	2
New Horizon Mine
Asset Retirement Obligation And Accrual For Environmental Loss Contingencies [Line Items]
Environmental reclamation obligations	$ 67.3
Discounted basis of environmental reclamation obligation	$ 36.8
Discount rate of environmental reclamation obligations (as a percent)	3.25%
Undiscounted future cash outflows of environmental reclamation obligations	$ 57.9
Regulatory item recognized		$ 44.9
Amortization period for portion of environmental reclamation obligations reversed		25 years