Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Retained earnings	Common stock	Treasury Stock	Additional paid-in capital	Accumulated other comprehensive (loss) income
Beginning Balance at Dec. 31, 2012	$ (369,465)	$ (130,030)	$ (213)	$ 0	$ (239,609)	$ 387
Beginning Balance, shares at Dec. 31, 2012			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)	0	(239,609)	1,494
Ending Balance, shares at Dec. 31, 2013			21,352,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	99,533	99,533
Currency translation	(1,035)					(1,035)
Postretirement plans	(2,820)					(2,820)
Short-term investments	0
Cash dividends declared	(34,164)	(34,164)
Ending Balance at Dec. 31, 2014	$ (495,416)	(260,943)	$ (213)	0	(239,609)	5,349
Ending Balance, shares at Dec. 31, 2014	21,352,297		21,352,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	$ 133,453	133,453
Currency translation	(1,955)					(1,955)
Postretirement plans	49					49
Short-term investments	0
Cash dividends declared	(33,243)	(33,243)
Treasury Stock, Shares, Acquired			(1,508,000)
Treasury Stock, Value, Acquired, Cost Method	(57,423)			(57,423)
Ending Balance at Dec. 31, 2015	$ (536,297)	$ (361,153)	$ (213)	$ (57,423)	$ (239,609)	$ 7,255
Ending Balance, shares at Dec. 31, 2015	19,844,531		19,844,000