Note 2 - Revision of Previously Issued Financial Statements - Impact of Error Corrections and Prior Period Adjustments (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Depreciation, depletion and amortization	$ 43,464	$ 29,518	$ 27,033	$ 30,435	$ 57,468	$ 103,335	$ 86,986	$ 120,599	$ 123,631
Total cost of sales	137,073	97,876	104,536	109,111	213,647	350,253	311,523	425,326	461,956
Gross profit	6,576	42,963	29,743	33,433	63,176	80,364	106,139	152,449	184,001
Income (loss) from operations	(30,376)	20,268	2,511	14,388	16,899	(14,671)	37,167	60,106	109,439
Foreign exchange (loss) gain	(2,212)	(4,917)	(3,080)	(2,260)	(5,340)	2,856	(10,258)	(9,680)	(2,737)
Total other (expense) income	4,513	(25,084)	(11,093)	(18,106)	(29,199)	10,317	(54,284)	(67,663)	(19,780)
(Loss) income before income taxes	(25,863)	(4,816)	(8,582)	(3,718)	(12,300)	(4,354)	(17,117)	(7,557)	89,659
Income tax benefit (provision)	2,679	5,130	(16,366)	28,800	12,434	1,484	17,564	(20,963)	(28,090)
Net Income (Loss) Attributable to Parent, Total	(23,184)	314	(24,948)	25,082	134	(2,870)	447	(28,520)	61,569
Income applicable to common shareholders	(23,322)	176	(25,086)	24,944	(142)	(3,284)	33	(29,072)	61,017
Comprehensive income	$ (19,438)	$ 7,950	$ (22,070)	$ 28,286	$ 6,216	$ (6,390)	$ 14,165	$ (17,291)	$ 59,598
Basic income per common share after preferred dividends (in dollars per share)	$ (0.05)		$ (0.06)	$ 0.07		$ (0.01)		$ (0.07)	$ 0.16
Diluted income per common share after preferred dividends (in dollars per share)	$ (0.05)		$ (0.06)	$ 0.07		$ (0.01)		$ (0.07)	$ 0.16
Debit - DDA expense				$ 31,073	$ 59,855	$ 108,814	$ 91,255	$ 126,467	$ 124,918
Foreign exchange loss (gain)				504	4,396	(2,032)	10,520	10,208	4,460
Deferred income taxes				(20,963)	(21,571)	(4,637)	(23,467)	19,392	2,774
Cash provided by operating activities				38,285	45,821	75,210	74,115	115,878	225,328
Debit - Inventories: concentrates, doré, and stockpiled ore	$ 42,464					42,464		29,366
Total current assets	198,329					198,329		321,236
Properties, plants, equipment and mineral interests, net	2,487,429					2,487,429		1,999,311
Total assets	2,710,258					2,710,258		2,345,158
Credit - Deferred tax liability	164,928					164,928		124,352
Total liabilities	988,189					988,189		883,881
Credit - Accumulated deficit	(223,280)					(223,280)		(218,089)
Total shareholders' equity	1,722,069					1,722,069		1,461,277
Total liabilities and shareholders' equity	$ 2,710,258					$ 2,710,258		2,345,158
Previously Reported [Member]
Depreciation, depletion and amortization		$ 28,844	$ 25,569	28,952	54,521		83,365	116,062	116,126
Total cost of sales		97,202	103,072	107,628	210,700		307,902	420,789	454,451
Gross profit		43,637	31,207	34,916	66,123		109,760	156,986	191,506
Income (loss) from operations		20,942	3,975	15,871	19,846		40,788	64,643	116,944
Foreign exchange (loss) gain		(4,764)	(3,883)	(2,262)	(6,145)		(10,909)	(10,300)	(2,926)
Total other (expense) income		(24,931)	(11,896)	(18,108)	(30,004)		(54,935)	(68,283)	(19,969)
(Loss) income before income taxes		(3,989)	(7,921)	(2,237)	(10,158)		(14,147)	(3,640)	96,975
Income tax benefit (provision)		5,401	(16,095)	29,071	12,976		18,377	(19,879)	(27,428)
Net Income (Loss) Attributable to Parent, Total		1,412	(24,016)	26,834	2,818		4,230	(23,519)	69,547
Income applicable to common shareholders		1,274	(24,154)	26,696	2,542		3,816	(24,071)	68,995
Comprehensive income		$ 9,048	$ (21,138)	$ 30,038	$ 8,900		$ 17,948	$ (12,290)	$ 67,576
Basic income per common share after preferred dividends (in dollars per share)			$ (0.06)	$ 0.07	$ 0.01		$ 0.01	$ (0.06)	$ 0.18
Diluted income per common share after preferred dividends (in dollars per share)			$ (0.06)	$ 0.07	$ 0.01		$ 0.01	$ (0.06)	$ 0.18
Debit - DDA expense				$ 29,590	$ 56,908		$ 87,634	$ 121,930	$ 117,413
Foreign exchange loss (gain)				506	5,201		11,171	10,828	4,649
Deferred income taxes				(21,234)	(22,113)		(24,280)	18,308	2,112
Cash provided by operating activities				38,285	45,821		74,115	115,878	225,328
Debit - Inventories: concentrates, doré, and stockpiled ore								28,455
Total current assets								320,325
Properties, plants, equipment and mineral interests, net								2,020,021
Total assets								2,364,957
Credit - Deferred tax liability								121,546
Total liabilities								881,075
Credit - Accumulated deficit								(195,484)
Total shareholders' equity								1,483,882
Total liabilities and shareholders' equity								2,364,957
Restatement Adjustment [Member]
Depreciation, depletion and amortization		$ 674	$ 1,464	1,483	2,947		3,621	4,537	7,505
Total cost of sales		674	1,464	1,483	2,947		3,621	4,537	7,505
Gross profit		(674)	(1,464)	(1,483)	(2,947)		(3,621)	(4,537)	(7,505)
Income (loss) from operations		(674)	(1,464)	(1,483)	(2,947)		(3,621)	(4,537)	(7,505)
Foreign exchange (loss) gain		(153)	803	2	805		651	620	189
Total other (expense) income		(153)	803	2	805		651	620	189
(Loss) income before income taxes		(827)	(661)	(1,481)	(2,142)		(2,970)	(3,917)	(7,316)
Income tax benefit (provision)		(271)	(271)	(271)	(542)		(813)	(1,084)	(662)
Net Income (Loss) Attributable to Parent, Total		(1,098)	(932)	(1,752)	(2,684)		(3,783)	(5,001)	(7,978)
Income applicable to common shareholders		(1,098)	(932)	(1,752)	(2,684)		(3,783)	(5,001)	(7,978)
Comprehensive income		$ (1,098)	$ (932)	$ (1,752)	$ (2,684)		$ (3,783)	$ (5,001)	$ (7,978)
Basic income per common share after preferred dividends (in dollars per share)					$ (0.01)		$ (0.01)	$ (0.01)	$ (0.02)
Diluted income per common share after preferred dividends (in dollars per share)					$ (0.01)		$ (0.01)	$ (0.01)	$ (0.02)
Debit - DDA expense				$ 1,483	$ 2,947		$ 3,621	$ 4,537	$ 7,505
Foreign exchange loss (gain)				(2)	(805)		(651)	(620)	(189)
Deferred income taxes				271	542		813	1,084	662
Cash provided by operating activities
Debit - Inventories: concentrates, doré, and stockpiled ore								911
Total current assets								911
Properties, plants, equipment and mineral interests, net								(20,710)
Total assets								(19,799)
Credit - Deferred tax liability								2,806
Total liabilities								2,806
Credit - Accumulated deficit								(22,605)
Total shareholders' equity								(22,605)
Total liabilities and shareholders' equity								$ (19,799)