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, 2018	Dec. 31, 2017
Property, plant and equipment, gross		$ 3,634,861	$ 2,974,092
Less accumulated depreciation, depletion and amortization		1,114,857	974,781
Net carrying value	[1]	2,520,004	1,999,311
Mining Properties Including Asset Retirement Obligations [Member]
Property, plant and equipment, gross		533,631	404,905
Mine Development [Member]
Property, plant and equipment, gross		444,229	390,094
Plant and Equipment [Member]
Property, plant and equipment, gross		988,285	847,462
Land [Member]
Property, plant and equipment, gross		32,953	26,949
Mineral Interests [Member]
Property, plant and equipment, gross		1,269,956	957,359
Construction in Progress [Member]
Property, plant and equipment, gross		$ 365,807	$ 347,323

[1] Amounts reported as of and for the years ended December 31, 2017 and 2016 have been revised. See Note 2 for more information.