Note 4 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments - Major Components of Property, Plants, Equipment and Mineral Interests (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, plant and equipment, gross	$ 3,824,404	$ 3,734,094
Less accumulated depreciation, depletion and amortization	1,479,185	1,310,396
Net carrying value	2,345,219	2,423,698
Mining Properties Including Asset Retirement Obligations [Member]
Property, plant and equipment, gross	818,819	762,355
Mine Development [Member]
Property, plant and equipment, gross	526,714	503,111
Plant and Equipment [Member]
Property, plant and equipment, gross	1,129,200	1,056,512
Land [Member]
Property, plant and equipment, gross	32,983	32,909
Mineral Interests [Member]
Property, plant and equipment, gross	969,589	1,018,380
Construction in Progress [Member]
Property, plant and equipment, gross	$ 347,099	$ 360,827

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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