Note 3 - Properties, Plants, Equipment and Mineral Interests, and Lease Commitments (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Property, Plant and Equipment [Table Text Block]

	December 31,
	2017		2016
Mining properties, including asset retirement obligations	$	443,182	$	403,935
Development costs		390,094		347,356
Plants and equipment		847,462		814,091
Land		26,949		26,229
Mineral interests		919,082		952,382
Construction in progress		347,323		330,785
		2,974,092		2,874,778
Less accumulated depreciation, depletion and amortization		954,071		842,093
Net carrying value	$	2,020,021	$	2,032,685

Lessee, Operating Lease, Disclosure [Table Text Block]

Year ending December 31,
2018	$	4,812
2019		2,864
2020		2,882
2021		2,881
2022		2,547
Thereafter		—
Total	$	15,986