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Inventories (Tables)
 3 Months Ended
Mar. 31, 2018
Inventory Disclosure [Abstract]  
Schedule of Inventory, Current
 
March 31, 2018
 
December 31, 2017
Raw materials
$
38,093

 
$
48,502

Work in progress
57,025

 
50,511

Finished goods
34,425

 
35,430

Spares and other
23,563

 
23,091

 
153,106

 
157,534

Reduction to LIFO cost basis
(28,471
)
 
(28,326
)
Total inventories – net
$
124,635

 
$
129,208