Note 11 - Commitments, Contingencies and Obligations (Details Textual) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 31, 2018	Dec. 31, 2014	Aug. 31, 2012	Jun. 30, 2011	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Environmental Remediation Expense					$ 7,564		$ 1,254	$ 12,297	$ 2,807
Contractual Obligation, Total					700			700
Finance Lease, Liability, Payment, Due, Total					15,094			15,094
Lessee, Operating Lease, Liability, to be Paid, Total					9,803			9,803
Performance Obligation Commitments [Member]
Surety Bonds					182,600			182,600
Letters of Credit Outstanding, Amount					21,000			21,000
Lucky Friday [Member]
Open Purchase Orders					8,500			8,500
Casa Berardi [Member]
Open Purchase Orders					500			500
Greens Creek [Member]
Open Purchase Orders					5,500			5,500
Nevada Operations [Member]
Open Purchase Orders					$ 4,700			$ 4,700
Johnny M Mine Area near San Mateo, New Mexico [Member]
Payment Of Response Costs		$ 1,100	$ 1,100
Estimated Response Costs	$ 9,600					$ 9,000				$ 6,100
Environmental Remediation Expense						$ 9,000
Carpenter Snow Creek Superfund Site, Cascade County, Montana [Member]
Estimated Response Costs				$ 4,500
Estimated Future Response Cost				$ 100,000