Inventories (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of inventories, at LIFO value
Finished goods	$ 23,563	$ 23,172
Raw materials	15,190	18,068
Total FIFO inventories	38,753	41,240
Reserve to adjust inventories to LIFO value	(23,719)	(23,719)
Total LIFO inventories	$ 15,034	$ 17,521