Note 3 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments (Details) - Major Components of Property, Plants, Equipment and Mineral Interests - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	$ 2,627,088	$ 2,455,261
Less accumulated depreciation, depletion and amortization	730,277	623,697
Net carrying value	1,896,811	1,831,564
Mining Properties Including Asset Retirement Obligations [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	372,935	336,962
Mine Development [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	291,780	250,340
Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	738,065	698,100
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	21,362	15,799
Mineral Interests [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	907,791	929,844
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	$ 295,155	$ 224,216