Note 2 - Revision of Previously Issued Financial Statements - Impact of Understatement of DDA (Details) - USD ($) $ 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
Debit - Inventories: concentrates, doré, and stockpiled ore	$ 42,464					$ 42,464		$ 29,366
Debit - Accumulated deficit	223,280					223,280		218,089
Debit - DDA expense				$ 31,073	$ 59,855	108,814	$ 91,255	126,467	$ 124,918
Credit - Net foreign exchange gain (loss)	2,212	$ 4,917	$ 3,080	2,260	5,340	(2,856)	10,258	9,680	2,737
Net Income (Loss) Attributable to Parent, Total	(23,184)	314	(24,948)	25,082	134	(2,870)	447	(28,520)	61,569
Restatement Adjustment [Member]
Debit - Inventories: concentrates, doré, and stockpiled ore								911
Debit - Accumulated deficit								22,605
Debit - DDA expense				1,483	2,947		3,621	4,537	7,505
Credit - Net foreign exchange gain (loss)		153	(803)	(2)	(805)		(651)	(620)	(189)
Net Income (Loss) Attributable to Parent, Total		$ (1,098)	$ (932)	$ (1,752)	$ (2,684)		$ (3,783)	$ (5,001)	$ (7,978)
Understatement of Accumulated Depreciation, Depletion and Amortization [Member] | Period from June 01, 2013 Through June 30, 2018 [Member]
Debit - DDA expense						5,000
Credit - Net foreign exchange gain (loss)						(200)
Net Income (Loss) Attributable to Parent, Total						(4,800)
Understatement of Accumulated Depreciation, Depletion and Amortization [Member] | Period from June 01, 2013 Through June 30, 2018 [Member] | Restatement Adjustment [Member]
Credit - Accumulated DDA (recorded within properties, plants, equipment and mineral interests, net)	(36,200)					(36,200)
Debit - Inventories: concentrates, doré, and stockpiled ore	1,100					1,100
Understatement of Accumulated Depreciation, Depletion and Amortization [Member] | At January 01, 2018 [Member] | Restatement Adjustment [Member]
Debit - Accumulated deficit	$ 30,300					$ 30,300