Note 2 - Revision of Previously Issued Financial Statements for Immaterial Misstatements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Depreciation, depletion and amortization	$ 45,790	$ 45,732	$ 46,742	$ 37,990	$ 36,687	$ 37,815	$ 92,474	$ 74,502	$ 138,918	$ 112,492	$ 148,110	$ 191,451	$ 131,820
Total cost of sales	158,332	156,052	143,451	141,015	128,245	123,535	299,503	251,780	457,835	392,795	530,773	639,436	483,970
Gross profit	35,228	61,931	67,401	58,688	38,110	13,390	129,332	51,500	164,560	110,188	161,100	33,830	75,031
Income from operations	(8,572)	29,133	41,038	36,515	13,905	(13,046)	70,171	1,536	61,599	38,051	66,978	(46,678)	(35,058)
Income before income and mining taxes	(5,512)	(1,386)	26,194	20,461	(9,371)	(16,229)	24,808	(25,600)	19,296	(5,139)	(1,258)	(113,227)	(29,196)
Income and mining tax benefit (provision)	4,533	4,134	(4,743)	(5,181)	(2,646)	405	(609)	(2,242)	3,924	(7,423)	(8,199)	18,318	2,445
Net income	(979)	2,748	21,451	15,280	(12,017)	(15,824)	24,199	(27,842)	23,220	(12,562)	(9,457)	(94,909)	(26,751)
Income applicable to common shareholders	(1,117)	2,610	21,313	15,142	(12,155)	(15,962)	23,923	(28,118)	22,806	(12,976)	(10,009)	(95,461)	(27,303)
Comprehensive income	$ (7,246)	$ 4,368	$ 23,283	$ 21,430	$ (1,633)	$ (35,159)	$ 27,651	$ (36,793)	$ 20,405	$ (15,363)	$ (5,036)	$ (89,750)	$ (44,558)
Basic income per common share after preferred dividends (in cents) (in dollars per share)	$ (0.002)	$ 0.005	$ 0.04	$ 0.029	$ (0.023)	$ (0.030)	$ 0.043	$ (0.054)	$ 0.043	$ (0.025)	$ (0.019)	$ (0.195)	$ (0.063)
Diluted income per common share after preferred dividends (in cents) (in dollars per share)	$ (0.002)	$ 0.005	$ 0.04	$ 0.028	$ (0.023)	$ (0.030)	$ 0.043	$ (0.054)	$ 0.042	$ (0.025)	$ (0.019)	$ (0.195)	$ (0.063)
Depreciation, Depletion and Amortization, Total			$ 46,957			$ 39,779	$ 92,861	$ 79,598	$ 139,800	$ 120,076	$ 155,006	$ 196,408	$ 138,681
Deferred income taxes			141			(2,762)	(7,745)	(3,949)		(4,578)			8,690
Cash provided by operating activities			37,936			4,927	124,240	42,453	166,982	115,892	180,793	120,866	94,221
Cost of sales and other direct production costs	$ 112,542			$ 103,025	$ 91,558	85,720		177,278	318,917	280,303	382,663	447,985	352,150
Inventories: Concentrates, doré, and stockpiled ore											57,567	30,078
Total current assets	310,280								310,280		284,312	178,838
Properties, plants, equipment and mineral interests, net	2,331,018								2,331,018		2,378,074	2,447,450
Total assets	2,674,417								2,674,417		2,700,210	2,660,774
Deferred tax liability	142,750								142,750		156,091	157,637
Total liabilities	931,442								931,442		986,425	964,240
Accumulated deficit	(362,023)								(362,023)		(368,074)	(349,220)
Total shareholders' equity	1,742,975	$ 1,748,425		1,702,782	1,666,176		1,748,425	1,666,176	1,742,975	1,702,782	1,713,785	1,696,534
Total liabilities and shareholders' equity	2,674,417								2,674,417		2,700,210	2,660,774
Deferred income taxes											(3,818)	9,087
Accrued taxes	8,557								8,557		5,774
Total current liabilities	$ 126,182								$ 126,182		147,210
Previously Reported [Member]
Depreciation, depletion and amortization		48,403	49,331	40,238	39,423	39,666	97,734	79,089		119,327	157,130	199,518	134,044
Total cost of sales		158,723	146,040	146,215	132,276	125,553	304,763	257,829		404,044	546,170	649,867	488,038
Gross profit		59,260	64,812	53,488	34,079	11,372	124,072	45,451		98,939	145,703	23,399	79,099
Income from operations		26,462	38,449	31,315	9,874	(15,064)	64,911	(4,513)		26,802	51,581	(57,109)	(39,126)
Income before income and mining taxes		(4,057)	23,605	15,261	(13,402)	(18,247)	19,548	(31,649)		(16,388)	(16,655)	(123,658)	(33,264)
Income and mining tax benefit (provision)		4,842	(4,634)	(1,633)	(626)	1,062	208	436		(1,197)	(135)	24,101	6,701
Net income		785	18,971	13,628	(14,028)	(17,185)	19,756	(31,213)		(17,585)	(16,790)	(99,557)	(26,563)
Income applicable to common shareholders		647	18,833	13,490	(14,166)	(17,323)	19,480	(31,489)		(17,999)	(17,342)	(100,109)	(27,115)
Comprehensive income		$ 2,405	$ 20,803	$ 19,778	$ (3,644)	$ (36,520)	$ 23,208	$ (40,164)		$ (20,386)	$ (12,369)	$ (94,398)	$ (44,370)
Basic income per common share after preferred dividends (in cents) (in dollars per share)		$ 0.001	$ 0.035	$ 0.026	$ (0.027)	$ (0.033)	$ 0.036	$ (0.060)		$ (0.034)	$ (0.033)	$ (0.204)	$ (0.063)
Diluted income per common share after preferred dividends (in cents) (in dollars per share)		$ 0.001	$ 0.035	$ 0.026	$ (0.027)	$ (0.033)	$ 0.036	$ (0.060)		$ (0.034)	$ (0.033)	$ (0.204)	$ (0.063)
Depreciation, Depletion and Amortization, Total			$ 49,546			$ 41,630	$ 98,121	$ 84,185		$ 126,911	$ 164,026	$ 204,475	$ 140,905
Deferred income taxes			32			(3,252)	(8,562)	(5,165)		(6,390)			6,278
Cash provided by operating activities			37,936			4,927	124,240	42,453		115,892	180,793	120,866	94,221
Cost of sales and other direct production costs				$ 105,977	$ 92,853	85,887		178,740		284,717	389,040	450,349	353,994
Inventories: Concentrates, doré, and stockpiled ore											57,936	30,364
Total current assets											284,681	179,124
Properties, plants, equipment and mineral interests, net											2,345,219	2,423,698
Total assets											2,667,724	2,637,308
Deferred tax liability											132,475	138,282
Total liabilities											965,384	944,885
Accumulated deficit											(379,519)	(353,331)
Total shareholders' equity											1,702,340	1,692,423
Total liabilities and shareholders' equity											2,667,724	2,637,308
Deferred income taxes											(5,505)	5,668
Accrued taxes											8,349
Total current liabilities											149,785
Revision of Prior Period, Adjustment [Member]
Depreciation, depletion and amortization		$ (2,671)	(2,589)	(2,248)	(2,736)	(1,851)	(5,260)	(4,587)		(6,835)	(9,020)	(8,067)	(2,224)
Total cost of sales		(2,671)	(2,589)	(5,200)	(4,031)	(2,018)	(5,260)	(6,049)		(11,249)	(15,397)	(10,431)	(4,068)
Gross profit		2,671	2,589	5,200	4,031	2,018	5,260	6,049		11,249	15,397	10,431	(4,068)
Income from operations		2,671	2,589	5,200	4,031	2,018	5,260	6,049		11,249	15,397	10,431	4,068
Income before income and mining taxes		2,671	2,589	5,200	4,031	2,018	5,260	6,049		11,249	15,397	10,431	4,068
Income and mining tax benefit (provision)		(708)	(109)	(3,548)	(2,020)	(657)	(817)	(2,678)		(6,226)	(8,064)	(5,783)	(4,256)
Net income		1,963	2,480	1,652	2,011	1,361	4,443	3,371		5,023	7,333	4,648	(188)
Income applicable to common shareholders		1,963	2,480	1,652	2,011	1,361	4,443	3,371		5,023	7,333	4,648	(188)
Comprehensive income		$ 1,963	$ 2,480	$ 1,652	$ 2,011	$ 1,361	$ 4,443	$ 3,371		$ 5,023	$ 7,333	$ 4,648	$ (188)
Basic income per common share after preferred dividends (in cents) (in dollars per share)		$ 0.004	$ 0.005	$ 0.003	$ 0.004	$ 0.003	$ 0.007	$ 0.006		$ 0.009	$ 0.014	$ 0.009	$ 0
Diluted income per common share after preferred dividends (in cents) (in dollars per share)		$ 0.004	$ 0.005	$ 0.002	$ 0.004	$ 0.003	$ 0.007	$ 0.006		$ 0.009	$ 0.014	$ 0.009	$ 0
Depreciation, Depletion and Amortization, Total			$ (2,589)			$ (1,851)	$ (5,260)	$ (4,587)		$ (6,835)	$ (9,020)	$ (8,067)	$ (2,224)
Deferred income taxes			109			490	817	1,216		1,812			2,412
Cash provided by operating activities			$ 0			0	$ 0	0		0	0	0	0
Cost of sales and other direct production costs				$ (2,952)	$ (1,295)	$ (167)		$ (1,462)		$ (4,414)	(6,377)	(2,364)	$ (1,844)
Inventories: Concentrates, doré, and stockpiled ore											(369)	(286)
Total current assets											(369)	(286)
Properties, plants, equipment and mineral interests, net											32,855	23,752
Total assets											32,486	23,466
Deferred tax liability											23,616	19,355
Total liabilities											21,041	19,355
Accumulated deficit											11,445	4,111
Total shareholders' equity											11,445	4,111
Total liabilities and shareholders' equity											32,486	23,466
Deferred income taxes											1,687	$ 3,419
Accrued taxes											(2,575)
Total current liabilities											$ (2,575)