Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2012	$ 231,694	$ 529	$ (970)	$ 163,579	$ 82,731	$ (14,175)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	75,256				75,256
Unrealized gain (loss) on derivatives	103					103
Unrealized gain on short-term investments	(27)					(27)
Pension and post-retirement liability	10,082					10,082
Cash dividends declared ($0.50, $0.375 and $0.50 per share of common stock for 2014, 2013 and 2012 respectively))	(20,009)				(20,009)
Cash dividend declared ($0.375 per share)	3,039			3,039
Excess tax benefit from equity compensation	1,380			1,380
Issuance of treasury stock	7,942		1,136
Proceeds from options exercised		5		6,801
Shares withheld for employee taxes related to vested restricted stock and stock units			(166)
vested restricted stock and stock units	(166)			0
Ending balance at Dec. 31, 2013	309,294	534	0	174,799	137,978	(4,017)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	121,540				121,540
Unrealized gain (loss) on derivatives	(55)					(55)
Unrealized gain on short-term investments	(14)					(14)
Pension and post-retirement liability	(15,732)					(15,732)
Cash dividends declared ($0.50, $0.375 and $0.50 per share of common stock for 2014, 2013 and 2012 respectively))	(26,967)				(26,967)
Cash dividend declared ($0.375 per share)	7,487			7,487
Excess tax benefit from equity compensation	3,813			3,813
Proceeds from options exercised	5,563	4	572	4,987
Shares withheld for employee taxes related to vested restricted stock and stock units	(614)	1	(615)
Repurchase of common stock	(499)		(499)
Ending balance at Dec. 31, 2014	403,816	539	(542)	191,086	232,551	(19,818)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,868				11,868
Unrealized gain (loss) on derivatives	53					53
Unrealized gain on short-term investments	47					47
Pension and post-retirement liability	3,547					3,547
Cash dividends declared ($0.50, $0.375 and $0.50 per share of common stock for 2014, 2013 and 2012 respectively))	(23,445)				(23,445)
Cash dividend declared ($0.375 per share)	3,857			3,857
Excess tax benefit from equity compensation	0
Proceeds from options exercised	473	0	744	(271)
Shares withheld for employee taxes related to vested restricted stock and stock units	(794)	0	(792)	(2)
Repurchase of common stock	(15,255)		(15,255)
Ending balance at Dec. 31, 2015	$ 384,167	$ 539	$ (15,845)	$ 194,670	$ 220,974	$ (16,171)