Consolidated Statement of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Balance, shares at Dec. 31, 2017		32,332				615
Balance, value at Dec. 31, 2017	$ 531,719	$ 323	$ 271,957	$ 274,562	$ (4,366)	$ (10,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,352			8,352
Foreign currency translation adjustment	110				110
Minimum pension and post retirement benefit plan adjustments, net of taxes of $4	27				27
Stock compensation expense	2,097		2,097
Stock options exercised, shares		13
Stock options exercised	226		226
Net settlement of restricted stock units, shares		53				24
Net settlement of restricted stock units	(850)	$ 1	(1)			$ (850)
Balance, shares at Mar. 31, 2018		32,398				639
Balance, value at Mar. 31, 2018	541,955	$ 324	274,279	283,538	(4,579)	$ (11,607)
Balance, shares at Dec. 31, 2017		32,332				615
Balance, value at Dec. 31, 2017	531,719	$ 323	271,957	274,562	(4,366)	$ (10,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50,692
Foreign currency translation adjustment	(1,538)
Balance, shares at Sep. 30, 2018		32,842				778
Balance, value at Sep. 30, 2018	582,875	$ 328	280,149	325,878	(6,174)	$ (17,306)
Balance, shares at Mar. 31, 2018		32,398				639
Balance, value at Mar. 31, 2018	541,955	$ 324	274,279	283,538	(4,579)	$ (11,607)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,837			22,837
Foreign currency translation adjustment	(1,787)				(1,787)
Minimum pension and post retirement benefit plan adjustments, net of taxes of $4	26				26
Stock compensation expense	2,731		2,731
Stock options exercised, shares		21
Stock options exercised	300		300
Awards of common shares (in shares)		2
Net settlement of restricted stock units, shares		334				128
Net settlement of restricted stock units	(5,166)	$ 3	(3)			$ (5,166)
Balance, shares at Jun. 30, 2018		32,755				767
Balance, value at Jun. 30, 2018	560,896	$ 327	277,307	306,375	(6,340)	$ (16,773)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,503			19,503
Foreign currency translation adjustment	139				139
Minimum pension and post retirement benefit plan adjustments, net of taxes of $4	27				27
Stock compensation expense	2,026		2,026
Stock options exercised, shares		50
Stock options exercised	817	$ 1	816
Net settlement of restricted stock units, shares		37				11
Net settlement of restricted stock units	(533)					$ (533)
Balance, shares at Sep. 30, 2018		32,842				778
Balance, value at Sep. 30, 2018	582,875	$ 328	280,149	325,878	(6,174)	$ (17,306)
Balance, shares at Dec. 31, 2018		32,887				796
Balance, value at Dec. 31, 2018	596,693	$ 329	282,525	338,995	(7,234)	$ (17,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,345			6,345
Foreign currency translation adjustment	842				842
Minimum pension and post retirement benefit plan adjustments, net of taxes of $4	12				12
Stock compensation expense	2,371		2,371
Stock options exercised, shares		12
Stock options exercised	139		139
Net settlement of restricted stock units, shares		127				59
Net settlement of restricted stock units	(2,151)	$ 1	(1)			$ (2,151)
Balance, shares at Mar. 31, 2019		33,026				855
Balance, value at Mar. 31, 2019	605,833	$ 330	285,034	346,922	(6,380)	$ (20,073)
Balance, shares at Dec. 31, 2018		32,887				796
Balance, value at Dec. 31, 2018	596,693	$ 329	282,525	338,995	(7,234)	$ (17,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50,734
Foreign currency translation adjustment	1,176
Balance, shares at Sep. 30, 2019		33,145				888
Balance, value at Sep. 30, 2019	657,213	$ 332	293,009	391,311	(6,022)	$ (21,417)
Balance, shares at Mar. 31, 2019		33,026				855
Balance, value at Mar. 31, 2019	605,833	$ 330	285,034	346,922	(6,380)	$ (20,073)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,913			19,913
Foreign currency translation adjustment	998				998
Minimum pension and post retirement benefit plan adjustments, net of taxes of $4	12				12
Stock compensation expense	3,720		3,720
Stock options exercised, shares		5
Stock options exercised	69		69
Awards of common shares (in shares)		8
Net settlement of restricted stock units, shares		62				25
Net settlement of restricted stock units	(998)	$ 1	(1)			$ (998)
Balance, shares at Jun. 30, 2019		33,101				880
Balance, value at Jun. 30, 2019	629,547	$ 331	288,822	366,835	(5,370)	$ (21,071)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,476			24,476
Foreign currency translation adjustment	(664)				(664)
Minimum pension and post retirement benefit plan adjustments, net of taxes of $4	12				12
Stock compensation expense	3,996		3,996
Stock options exercised, shares		16
Stock options exercised	192		192
Net settlement of restricted stock units, shares		28				8
Net settlement of restricted stock units	(346)	$ 1	(1)			$ (346)
Balance, shares at Sep. 30, 2019		33,145				888
Balance, value at Sep. 30, 2019	$ 657,213	$ 332	$ 293,009	$ 391,311	$ (6,022)	$ (21,417)