Note 10 - Commitments, Contingencies and Obligations (Details Textual) - USD ($) $ in Thousands		1 Months Ended				3 Months Ended			6 Months Ended		12 Months Ended
	Oct. 30, 2019	Jul. 31, 2018	Dec. 31, 2014	Aug. 31, 2012	Jun. 30, 2011	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Environmental Remediation Expense						$ 1,024		$ 1,037	$ 4,733	$ 1,553
Contractual Obligation, Total						1,400			1,400
Finance Lease, Liability, Payment, Due, Total						16,153			16,153
Lessee, Operating Lease, Liability, to be Paid, Total						10,705			10,705
Performance Obligation Commitments [Member]
Surety Bonds						180,200			180,200
Letters of Credit Outstanding, Amount						19,900			19,900
Lucky Friday [Member]
Open Purchase Orders						5,800			5,800
Casa Berardi [Member]
Open Purchase Orders						600			600
Greens Creek [Member]
Open Purchase Orders						6,800			6,800
Nevada Operations [Member]
Open Purchase Orders						$ 3,600			$ 3,600
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