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Inventories (Narrative) (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Inventory Disclosure [Abstract]    
Percentage of LIFO inventory 63.00% 67.00%
Excess of current costs over stated LIFO value $ 8,123 $ 8,123
Inventory obsolescence reserves $ 7,721 $ 7,262