Income and Mining Taxes - Summary of Tax Credit Carryforwards (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Tax Credit Carryforward [Line Items]
Regular net operating losses	$ 877,458
Capital losses	63,024
Foreign tax credits	24,939
United States
Tax Credit Carryforward [Line Items]
Regular net operating losses	432,447
Capital losses	63,024
Foreign tax credits	24,939
Canada
Tax Credit Carryforward [Line Items]
Regular net operating losses	304,237
Mexico
Tax Credit Carryforward [Line Items]
Regular net operating losses	52,951
New Zealand
Tax Credit Carryforward [Line Items]
Regular net operating losses	86,486
Other jurisdictions
Tax Credit Carryforward [Line Items]
Regular net operating losses	$ 1,337