CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - UNAUDITED - USD ($) $ in Thousands	Total	Common Stock	Additional Contributed Capital	Retained Earnings	Accumulated Other Comprehensive Earnings/(Loss)	Treasury Stock
Beginning Balance at Dec. 31, 2018	$ 377,929	$ 306,697	$ 42,820	$ 478,847	$ (97,739)	$ (352,696)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	11,419			11,419
Changes in fair market value of derivatives, net of tax	78				78
Changes in unrealized pension cost, net of tax	1,022				1,022
Cumulative translation adjustment, net of tax	91				91
Cash dividends	(1,315)			(1,315)
Acquired shares for treasury stock	(849)					(849)
Issued shares on vesting of restricted stock units	(2,636)	967	(3,603)
Stock compensation	1,154		1,154
Ending Balance at Mar. 31, 2019	386,893	307,664	40,371	488,951	(96,548)	(353,545)
Beginning Balance at Dec. 31, 2018	377,929	306,697	42,820	478,847	(97,739)	(352,696)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	26,084
Changes in fair market value of derivatives, net of tax	(956)
Changes in unrealized pension cost, net of tax	3,065
Cumulative translation adjustment, net of tax	(88)
Acquired shares for treasury stock	(8,045)
Ending Balance at Sep. 30, 2019	395,194	307,801	42,849	501,003	(95,718)	(360,741)
Beginning Balance at Mar. 31, 2019	386,893	307,664	40,371	488,951	(96,548)	(353,545)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	11,943			11,943
Changes in fair market value of derivatives, net of tax	(294)				(294)
Changes in unrealized pension cost, net of tax	1,026				1,026
Cumulative translation adjustment, net of tax	(87)				(87)
Cash dividends	(1,309)			(1,309)
Acquired shares for treasury stock	(4,153)					(4,153)
Issued shares on vesting of restricted stock units		111	(111)
Stock compensation	1,526		1,526
Ending Balance at Jun. 30, 2019	395,545	307,775	41,786	499,585	(95,903)	(357,698)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	2,722			2,722
Changes in fair market value of derivatives, net of tax	(740)				(740)
Changes in unrealized pension cost, net of tax	1,017				1,017
Cumulative translation adjustment, net of tax	(92)				(92)
Cash dividends	(1,304)			(1,304)
Acquired shares for treasury stock	(3,043)					(3,043)
Issued shares on vesting of restricted stock units	(15)	26	(41)
Stock compensation	1,104		1,104
Ending Balance at Sep. 30, 2019	395,194	307,801	42,849	501,003	(95,718)	(360,741)
Beginning Balance at Dec. 31, 2019	405,219	307,932	43,689	509,766	(91,726)	(364,442)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	3,808			3,808
Changes in fair market value of derivatives, net of tax	(4,414)				(4,414)
Changes in unrealized pension cost, net of tax	1,285				1,285
Cumulative translation adjustment, net of tax	(139)				(139)
Cash dividends	(1,298)			(1,298)
Acquired shares for treasury stock	(5,304)					(5,304)
Issued shares on vesting of restricted stock units	(1,903)	2,166	(4,069)
Stock compensation	212		212
Ending Balance at Mar. 31, 2020	397,466	310,098	39,832	512,276	(94,994)	(369,746)
Beginning Balance at Dec. 31, 2019	405,219	307,932	43,689	509,766	(91,726)	(364,442)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	19,738
Changes in fair market value of derivatives, net of tax	(2,861)
Changes in unrealized pension cost, net of tax	3,733
Cumulative translation adjustment, net of tax	(54)
Acquired shares for treasury stock	(8,080)
Ending Balance at Sep. 30, 2020	413,966	310,976	40,796	525,624	(90,908)	(372,522)
Beginning Balance at Mar. 31, 2020	397,466	310,098	39,832	512,276	(94,994)	(369,746)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	4,857			4,857
Changes in fair market value of derivatives, net of tax	644				644
Changes in unrealized pension cost, net of tax	1,209				1,209
Cumulative translation adjustment, net of tax	(14)				(14)
Cash dividends	(1,292)			(1,292)
Acquired shares for treasury stock	(2,776)					(2,776)
Issued shares on vesting of restricted stock units		855	(855)
Stock compensation	798		798
Ending Balance at Jun. 30, 2020	400,892	310,953	39,775	515,841	(93,155)	(372,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	11,073			11,073
Changes in fair market value of derivatives, net of tax	909				909
Changes in unrealized pension cost, net of tax	1,239				1,239
Cumulative translation adjustment, net of tax	99				99
Cash dividends	(1,290)			(1,290)
Issued shares on vesting of restricted stock units	(8)	23	(31)
Stock compensation	1,052		1,052
Ending Balance at Sep. 30, 2020	$ 413,966	$ 310,976	$ 40,796	$ 525,624	$ (90,908)	$ (372,522)