CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income Statement [Abstract]
Net sales	$ 142,774	$ 153,293
Cost of goods sold	(130,213)	(137,220)
Gross margin	12,561	16,073
Other operating income (expense):
Selling expense	(2,135)	(2,086)
General and administrative expense	(4,634)	(5,137)
Defined benefit pension credit	3,696	1,899
Other postretirement benefit credit	1,674	1,577
Total other operating expense	(1,399)	(3,747)
Operating income	11,162	12,326
Nonoperating income (expense):
Interest expense	(345)	(360)
Other income (expense), net	75	(277)
Total nonoperating expense	(270)	(637)
Income before income taxes	10,892	11,689
Provision for income taxes	(4,225)	(4,424)
Net income	$ 6,667	$ 7,265
Basic and diluted income per share	$ 0.55	$ 0.60
Basic and diluted weighted average shares outstanding	12,102	12,102