Note 13 - Property and Equipment, Net - Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Property and equipment, gross	$ 1,457,754	$ 1,459,485	$ 1,422,394
Less: accumulated depreciation and depletion	922,796	917,188	869,890
Property and equipment, net	534,958	542,297	552,504
Equipment and Vehicles [Member]
Property and equipment, gross	942,116	947,687	915,748
Mining Properties and Mineral Rights [Member]
Property and equipment, gross	188,380	188,960	191,805
Land and Land Improvements [Member]
Property and equipment, gross	134,147	132,531	140,078
Building and Building Improvements [Member]
Property and equipment, gross	124,784	122,316	108,587
Furniture and Fixtures [Member]
Property and equipment, gross	$ 68,327	$ 67,991	$ 66,176

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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