Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Retained earnings	Common stock	Additional paid-in capital	Accumulated other comprehensive (loss) income
Beginning Balance at Dec. 31, 2010	$ 307,776	$ 67,209	$ 213	$ 238,947	$ 1,407
Beginning Balance, shares at Dec. 31, 2010			21,316,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	4,336	4,336
Currency translation	(285)				(285)
Postretirement plans	(2,320)				(2,320)
Proceeds from stock options exercises	756			756
Proceeds from stock options exercises, shares			36,000
Tax deficiency related to stock option exercises	(94)			(94)
Short-term investments	0
Ending Balance at Dec. 31, 2011	310,169	71,545	213	239,609	(1,198)
Ending Balance, shares at Dec. 31, 2011			21,352,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	63,823	63,823
Currency translation	279				279
Postretirement plans	(681)				(681)
Short-term investments	1,213				1,213
Cash dividends declared	(5,338)	(5,338)
Ending Balance at Dec. 31, 2012	369,465	130,030	213	239,609	(387)
Ending Balance, shares at Dec. 31, 2012	21,352,297		21,352,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	86,896	86,896
Currency translation	(802)				(802)
Postretirement plans	908				908
Short-term investments	(1,213)				(1,213)
Cash dividends declared	(21,352)	(21,352)
Ending Balance at Dec. 31, 2013	$ 433,902	$ 195,574	$ 213	$ 239,609	$ (1,494)
Ending Balance, shares at Dec. 31, 2013	21,352,297		21,352,000