v3.7.0.1
PROPERTY, PLANT, EQUIPMENT, AND MINERAL PROPERTIES (Schedule of Property, Plant, Equipment, and Mineral Properties) (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Property, plant, equipment, and mineral properties    
Depreciable assets $ 377,333 $ 385,173
Accumulated depreciation (121,559) (116,194)
Depreciable assets, net 255,774 268,979
Mineral properties and development costs 138,785 138,578
Accumulated depletion (23,742) (21,974)
Total depletable assets, net 115,043 116,604
Land 519 719
Construction in progress 2,957 2,188
Total property, plant, equipment and mineral properties, net 374,293 388,490
Buildings Plant    
Property, plant, equipment, and mineral properties    
Depreciable assets 79,432 82,457
Machinery and Equipment    
Property, plant, equipment, and mineral properties    
Depreciable assets 225,570 227,987
Vehicles    
Property, plant, equipment, and mineral properties    
Depreciable assets 4,743 4,750
Office Equipment and Improvements    
Property, plant, equipment, and mineral properties    
Depreciable assets 12,598 12,505
Ponds and Land Improvements    
Property, plant, equipment, and mineral properties    
Depreciable assets $ 54,990 $ 57,474