Income and Mining Taxes - Summary of Tax Credit Carryforwards (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Tax Credit Carryforward [Line Items]
Regular net operating losses	$ 794,539
Capital losses	82,147
Alternative minimum tax credits	430
Foreign tax credits	24,939
United States
Tax Credit Carryforward [Line Items]
Regular net operating losses	421,561
Capital losses	82,147
Alternative minimum tax credits	430
Foreign tax credits	24,939
Canada
Tax Credit Carryforward [Line Items]
Regular net operating losses	236,849
Capital losses	0
Alternative minimum tax credits	0
Foreign tax credits	0
Mexico
Tax Credit Carryforward [Line Items]
Regular net operating losses	52,947
Capital losses	0
Alternative minimum tax credits	0
Foreign tax credits	0
New Zealand
Tax Credit Carryforward [Line Items]
Regular net operating losses	80,838
Capital losses	0
Alternative minimum tax credits	0
Foreign tax credits	0
Other jurisdictions
Tax Credit Carryforward [Line Items]
Regular net operating losses	2,344
Capital losses	0
Alternative minimum tax credits	0
Foreign tax credits	$ 0