Note 3 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total Capital Expenditures Excluding Capital Leases	$ 164.8
Accumulated Capitalized Interest Costs	16.2	$ 13.5
Capital Leased Assets, Gross	42.2	39.9
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	26.0	24.4
Operating Leases, Rent Expense	4.8	$ 3.8	$ 3.5
Lucky Friday [Member]
Total Capital Expenditures Excluding Capital Leases	41.5
Greens Creek [Member]
Total Capital Expenditures Excluding Capital Leases	47.0
Casa Berardi [Member]
Total Capital Expenditures Excluding Capital Leases	70.1
San Sebastian [Member]
Total Capital Expenditures Excluding Capital Leases	$ 1.6