Note 15 - Acquisitions - Unaudited Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mines Management [Member]
Sales of products	$ 645,957	$ 443,567
Net income (loss)	68,778	(89,806)
Income (loss) applicable to common shareholders	$ 68,226	$ (90,357)
Basic and diluted income (loss) per common share (in dollars per share)	$ 0.17	$ (0.24)
Revett Mining Company, Inc. [Member]
Sales of products			$ 445,703
Net income (loss)			(89,118)
Income (loss) applicable to common shareholders			$ (89,670)
Basic and diluted income (loss) per common share (in dollars per share)			$ (0.24)