Income and Mining Taxes - Income and Mining Tax (Expense) Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Current Other Tax Expense (Benefit)	$ (3)	$ 67	$ 55
Deferred Other Tax Expense (Benefit)	0	(449)	1,560
Income tax (expense) benefit	11,129	16,780	(28,998)
United States
Income Tax Examination [Line Items]
Deferred federal income tax expense (benefit)	(236)	(23,322)	(6,367)
United States - Alternative Minimum tax
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	334	(1,188)	(1,428)
United States — State mining taxes
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	4,001	3,208	6,016
Deferred federal income tax expense (benefit)	(251)	(1,134)	(1,052)
United States — Foreign withholding tax
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	1,598	5,617	8,466
Canada
Income Tax Examination [Line Items]
Current foreign tax expense (benefit)	(119)	(378)	(876)
Deferred foreign income tax expense (benefit)	(32,084)	(16,057)	(104)
Mexico
Income Tax Examination [Line Items]
Current foreign tax expense (benefit)	19,619	26,021	30,763
Deferred foreign income tax expense (benefit)	$ (3,994)	$ (9,929)	$ (4,805)