Accumulated Other Comprehensive Income (Loss) (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss)
Cost of product sold	$ 303,433	$ 325,876
Selling, general and administrative expenses	13,607	14,742
Total before tax	(444)	(394)
Post retirement medical plan | Amount Reclassified from Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss)
Cost of product sold	371	331
Selling, general and administrative expenses	73	63
Total before tax	444	394
Tax benefit	(160)	(142)
Amounts reclassified from accumulated other comprehensive income	$ 284	$ 252