Note 3 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments (Details) - Major Components of Property, Plants, Equipment and Mineral Interests (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	$ 2,455,261	$ 2,306,972
Less accumulated depreciation, depletion and amortization	623,697	515,371
Net carrying value	1,831,564	1,791,601
Mining Properties Including Asset Retirement Obligations [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	336,962	312,692
Mine Development [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	250,340	204,598
Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	698,100	626,818
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	15,799	15,799
Mineral Interests [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	929,844	946,144
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plants, equipment, and minerals	$ 224,216	$ 200,921