Note 4 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Property, Plant and Equipment [Table Text Block]

	December 31,
	2018		2017
			Revised
Mining properties, including asset retirement obligations	$	533,631	$	404,905
Development costs		444,229		390,094
Plants and equipment		988,285		847,462
Land		32,953		26,949
Mineral interests		1,269,956		957,359
Construction in progress		365,807		347,323
		3,634,861		2,974,092
Less accumulated depreciation, depletion and amortization		1,114,857		974,781
Net carrying value	$	2,520,004	$	1,999,311

Lessee, Operating Lease, Disclosure [Table Text Block]

Year ending December 31,
2019	$	7,919
2020		5,530
2021		3,578
2022		2,543
2023		2,182
Thereafter		1,397
Total	$	23,149