Note 4 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Payments to Acquire Property, Plant, and Equipment, Total	$ 136,933	$ 98,038	$ 164,788
Accumulated Capitalized Interest Costs		900
Capital Leased Assets, Gross, Total	58,400	48,600
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	38,400	33,100
Operating Leases, Rent Expense, Total	7,800	$ 4,800	$ 4,800
Lucky Friday [Member]
Payments to Acquire Property, Plant, and Equipment, Total	14,200
Greens Creek [Member]
Payments to Acquire Property, Plant, and Equipment, Total	40,900
Mining Assets, Value Beyond Proven and Probable Reserves (VBPP)	223,400
Casa Berardi [Member]
Payments to Acquire Property, Plant, and Equipment, Total	39,700
Mining Assets, Value Beyond Proven and Probable Reserves (VBPP)	396,400
San Sebastian [Member]
Payments to Acquire Property, Plant, and Equipment, Total	6,200
Nevada Operations [Member]
Payments to Acquire Property, Plant, and Equipment, Total	32,600
Mining Assets, Value Beyond Proven and Probable Reserves (VBPP)	$ 382,100