Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Balance, shares at Dec. 31, 2016		32,085,000				530,000
Balance at Dec. 31, 2016	$ 460,880	$ 320	$ 264,418	$ 211,748	$ (7,721)	$ (7,885)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	62,560			62,560
Foreign currency translation adjustment	3,150				3,150
Adjustment to post-retirement healthcare benefit liability, net of taxes	205				205
Stock compensation expense	7,122		7,122
Net settlement of restricted stock units, shares		203,000				85,000
Net settlement of restricted stock units	$ (2,872)	$ 3	(3)			$ (2,872)
Issuance of restricted stock, shares		2,000
Stock options exercised, shares	42,058	42,000
Stock options exercised	$ 674		674
Balance, shares at Dec. 31, 2017		32,332,000				615,000
Balance at Dec. 31, 2017	531,719	$ 323	271,957	274,562	(4,366)	$ (10,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	63,809			63,809
Foreign currency translation adjustment	(3,241)				(3,241)
Adjustment to post-retirement healthcare benefit liability, net of taxes	723				723
Stock compensation expense	9,189		9,189
Net settlement of restricted stock units, shares		460,000				181,000
Net settlement of restricted stock units	(7,165)	$ 5	(5)			$ (7,165)
Issuance of restricted stock, shares		7,000
Stock options exercised, shares		88,000
Stock options exercised	1,385	$ 1	1,384
Balance, shares at Dec. 31, 2018		32,887,000				796,000
Balance at Dec. 31, 2018	596,693	$ 329	282,525	338,995	(7,234)	$ (17,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	65,091			65,091
Foreign currency translation adjustment	1,766				1,766
Adjustment to post-retirement healthcare benefit liability, net of taxes	77				77
Stock compensation expense	12,570		12,570
Net settlement of restricted stock units, shares		255,000				110,000
Net settlement of restricted stock units	$ (4,305)	$ 3	(3)			$ (4,305)
Issuance of restricted stock, shares		8,000
Stock options exercised, shares	42,350	42,000
Stock options exercised	$ 490		490
Balance, shares at Dec. 31, 2019		33,192,000				906,000
Balance at Dec. 31, 2019	$ 673,964	$ 332	$ 295,582	$ 405,668	$ (5,391)	$ (22,227)