INVENTORY AND LONG-TERM PARTS INVENTORY (Tables)
 9 Months Ended
Sep. 30, 2016
Inventory Disclosure [Abstract]  
Summary of Inventory
The following summarizes our inventory, recorded at the lower of weighted average cost or estimated net realizable value, as of September 30, 2016, and December 31, 2015 (in thousands):
 
 
September 30, 2016
 
December 31, 2015
Finished goods product inventory
 
$
56,118

 
$
65,200

In-process mineral inventory
 
26,961

 
19,769

Total product inventory
 
83,079

 
84,969

Current parts inventory, net
 
18,819

 
21,562

Total current inventory, net
 
101,898

 
106,531

Long-term parts inventory, net
 
20,535

 
17,344

Total inventory, net
 
$
122,433

 
$
123,875