Income and Mining Taxes - Income and Mining Tax (Expense) Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Examination [Line Items]
Current Other Tax Expense (Benefit)	$ (67)	$ (55)	$ (24)
Income tax (expense) benefit	(16,780)	28,998	(33,247)
United States
Income Tax Examination [Line Items]
Deferred federal income tax expense (benefit)	23,322	6,367	(1,610)
United States - Alternative Minimum tax [Member]
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	1,188	1,428	0
United States — State mining taxes
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	(3,208)	(6,016)	(7,826)
Deferred federal income tax expense (benefit)	1,134	1,052	748
United States — Foreign withholding tax
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	(5,617)	(8,466)	(1,838)
Australia
Income Tax Examination [Line Items]
Deferred Other Tax Expense (Benefit)	449	(1,560)	1,550
Canada
Income Tax Examination [Line Items]
Current foreign tax expense (benefit)	378	876	(1,841)
Deferred foreign income tax expense (benefit)	16,057	104	1,338
Mexico
Income Tax Examination [Line Items]
Current foreign tax expense (benefit)	(26,021)	(30,763)	(9,581)
Deferred foreign income tax expense (benefit)	$ 9,929	$ 4,805	$ 55,383