Income and Mining Taxes - Income and Mining Tax (Expense) Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Examination [Line Items]
Current Other Tax Expense (Benefit)	$ 33	$ (3)	$ 67
Deferred Other Tax Expense (Benefit)	0	0	(449)
Income tax (expense) benefit	(37,045)	11,129	16,780
United States
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	(226)	334	(1,188)
Deferred federal income tax expense (benefit)	49	(236)	(23,322)
United States — State mining taxes
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	8,384	4,001	3,208
Deferred federal income tax expense (benefit)	354	(251)	(1,134)
United States — Foreign withholding tax
Income Tax Examination [Line Items]
Current federal tax expense (benefit)	800	1,598	5,617
Canada
Income Tax Examination [Line Items]
Current foreign tax expense (benefit)	(232)	(119)	(378)
Deferred foreign income tax expense (benefit)	0	(32,084)	(16,057)
Mexico
Income Tax Examination [Line Items]
Current foreign tax expense (benefit)	36,066	19,619	26,021
Deferred foreign income tax expense (benefit)	$ (8,117)	$ (3,994)	$ (9,929)