Note 10 - Commitments, Contingencies and Obligations (Details Textual) - USD ($) $ in Thousands		1 Months Ended				3 Months Ended		12 Months Ended
	Oct. 30, 2019	Jul. 31, 2018	Dec. 31, 2014	Aug. 31, 2012	Jun. 30, 2011	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Environmental Remediation Expense						$ 3,709	$ 516
Contractual Obligation, Total						2,100
Finance Lease, Liability, Payment, Due, Total						18,180
Lessee, Operating Lease, Liability, to be Paid, Total						11,691
Performance Obligation Commitments [Member]
Surety Bonds						176,800
Letters of Credit Outstanding, Amount						20,300
Lucky Friday [Member]
Open Purchase Orders						4,000
Casa Berardi [Member]
Open Purchase Orders						700
Greens Creek [Member]
Open Purchase Orders						2,800
Nevada Operations [Member]
Open Purchase Orders						2,700
PRP Lawsuit in Mineral County, Colorado [Member]
Loss Contingency, Damages Sought, Value	$ 5,000
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