Note 14 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments - Major Components of Property, Plants, Equipment and Mineral Interests (Details) - USD ($) $ in Thousands	Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Property, plant and equipment, gross	$ 3,909,019		$ 3,824,404
Less accumulated depreciation, depletion and amortization	1,598,209		1,446,330
Net carrying value	2,310,810	[1]	2,378,074	[1]	$ 2,447,450
Mining Properties Including Asset Retirement Obligations [Member]
Property, plant and equipment, gross	818,582		818,819
Mine Development [Member]
Property, plant and equipment, gross	549,666		526,714
Plant and Equipment [Member]
Property, plant and equipment, gross	1,446,183		1,410,209
Land [Member]
Property, plant and equipment, gross	34,931		32,983
Mineral Interests [Member]
Property, plant and equipment, gross	972,754		969,589
Construction in Progress [Member]
Property, plant and equipment, gross	$ 86,903		$ 66,090

[1] Amounts reported as of and for the years ended December 31, 2020 and 2019 have been revised. See Note 3 for more information.