Note 7 - Business Segments and Sales of Products - Information About Reportable Segments (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
Net sales	$ 143,649	$ 140,839				$ 430,617	$ 417,662
Income (loss) from operations	(30,376)	20,268	$ 2,511	$ 14,388	$ 16,899	(14,671)	37,167	$ 60,106	$ 109,439
Greens Creek [Member]
Net sales	65,187	61,062				205,642	191,250
Income (loss) from operations	10,705	16,575				59,373	46,107
Lucky Friday [Member]
Net sales	(11)	199				8,253	20,022
Income (loss) from operations	(5,404)	(4,642)				(14,811)	(8,974)
Casa Berardi [Member]
Net sales	52,850	53,989				164,501	139,524
Income (loss) from operations	(1,146)	2,208				3,118	(4,692)
San Sebastian [Member]
Net sales	14,129	25,589				40,727	66,866
Income (loss) from operations	(2,381)	17,017				2,275	42,363
Nevada Operations [Member]
Net sales	11,494					11,494
Income (loss) from operations	(13,741)					(13,741)
Other Segments [Member]
Income (loss) from operations	$ (18,409)	$ (10,890)				$ (50,885)	$ (37,637)