Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-In Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock
Balance, shares at Dec. 31, 2017			32,332,000						615,000
Balance at Dec. 31, 2017	$ 531,719	$ 274	$ 323	$ 271,957	$ 274,562	$ 624	$ (4,366)	$ (350)	$ (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	87,907		88,000
Stock options exercised	$ 1,385			1,384
Balance, shares at Dec. 31, 2018			32,887,000						796,000
Balance at Dec. 31, 2018	596,693	1,582	$ 329	282,525	338,995	1,582	(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
Accounting standards update	us-gaap:AccountingStandardsUpdate201602Member
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			42,000
Stock options exercised	490			490
Balance, shares at Dec. 31, 2019			33,192,000						906,000
Balance at Dec. 31, 2019	673,964	$ (291)	$ 332	295,582	405,668	$ (291)	(5,391)		$ (22,227)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,566				64,566
Foreign currency translation adjustment	3,301						3,301
Adjustment to post-retirement healthcare benefit liability, net of taxes	(371)						(371)
Stock compensation expense	$ 8,173			8,173
Accounting standards update	us-gaap:AccountingStandardsUpdate201613Member
Net settlement of restricted stock units, shares			296,000						122,000
Net settlement of restricted stock units	$ (6,656)		$ 4	(4)					$ (6,656)
Issuance of restricted stock, shares			4,000
Stock options exercised, shares	75,909		76,000
Stock options exercised	$ 1,119			1,119
Balance, shares at Dec. 31, 2020			33,568,000						1,028,000
Balance at Dec. 31, 2020	$ 743,805		$ 336	$ 304,870	$ 469,943		$ (2,461)		$ (28,883)