Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Operating activities:
Net income (loss)	$ (979)	$ 21,451	$ 15,280	$ (15,824)	$ 24,199	$ (27,842)	$ 23,220	$ (12,562)	$ (9,457)	$ (94,909)
Non-cash elements included in net income (loss):
Depreciation, depletion and amortization		46,957		39,779	92,861	79,598	139,800	120,076	155,006	196,408
Gain on exchange of investments	0		0				(1,158)	0
Unrealized loss (gain) on investments	2,861		(3,979)				7,117	(9,410)
Write-down to stockpile inventory							6,524	0
Provision for reclamation and closure costs							7,821	4,638
Stock compensation							4,774	5,229
Deferred income taxes							(17,886)	(4,578)
Amortization of loan origination fees							1,406	3,066
(Gain) loss on derivative contracts							(13,937)	4,483
Foreign exchange loss (gain)							615	(2,810)
Foundation grant	0		0				0	1,970
Other non-cash items, net							(239)	559
Change in assets and liabilities, net of business acquisitions:
Accounts receivable							(3,798)	(3,741)
Inventories							22,372	(13,090)
Other current and non-current assets							1,650	6,748
Accounts payable and accrued liabilities							(14,689)	(1,762)
Accrued payroll and related benefits							(1,829)	11,317
Accrued taxes							2,730	3,276
Accrued reclamation and closure costs and other non-current liabilities							2,489	2,483
Cash provided by operating activities		37,936		4,927	124,240	42,453	166,982	115,892	180,793	120,866
Investing activities:
Additions to properties, plants, equipment and mineral interests							(80,210)	(54,382)
Purchase of carbon credits							(200)	0
Proceeds from exchange of investments							1,811	0
Proceeds from disposition of properties, plants, equipment and mineral interests							562	305
Purchases of investments							0	(1,661)
Net cash used in investing activities							78,037	55,738
Financing activities:
Acquisition of treasury shares							(4,525)	(2,745)
Dividends paid to common shareholders							(16,755)	(3,951)
Dividends paid to preferred shareholders							(414)	(414)
Credit facility and debt issuance fees							(108)	(1,287)
Borrowings on debt							0	707,107
Repayments of debt							0	(716,500)
Repayments of finance leases							(5,598)	(4,246)
Net cash used in financing activities							(27,400)	(22,036)
Effect of exchange rates on cash							(471)	(1,873)
Net increase in cash, cash equivalents and restricted cash and cash equivalents							61,074	36,245
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period		$ 130,883		$ 63,477	$ 130,883	$ 63,477	130,883	63,477	63,477
Cash, cash equivalents and restricted cash and cash equivalents at end of period	$ 191,957		$ 99,722				191,957	99,722	$ 130,883	$ 63,477
Supplemental disclosure of cash flow information:
Cash paid for interest							37,173	33,828
Cash paid (received) for income and mining taxes							10,299	(2,608)
Significant non-cash investing and financing activities:
Addition of finance lease obligations							4,006	5,747
Payment of accrued compensation in stock							$ 0	$ 5,095