CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - UNAUDITED - USD ($) $ in Thousands	Total	Common Stock	Additional Contributed Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
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	8,665
Changes in fair market value of derivatives, net of tax	(3,770)
Changes in unrealized pension cost, net of tax	2,494
Cumulative translation adjustment, net of tax	(153)
Acquired shares for treasury stock	(8,080)
Ending Balance at Jun. 30, 2020	400,892	310,953	39,775	515,841	(93,155)	(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)
Beginning Balance at Dec. 31, 2020	423,682	311,190	41,654	539,281	(95,921)	(372,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	11,990			11,990
Changes in fair market value of derivatives, net of tax	124				124
Changes in unrealized pension cost, net of tax	1,422				1,422
Cumulative translation adjustment, net of tax	12				12
Cash dividends	(1,294)			(1,294)
Issued shares on vesting of restricted stock units	(1,400)	1,818	(3,218)
Stock compensation	1,180		1,180
Ending Balance at Mar. 31, 2021	435,716	313,008	39,616	549,977	(94,363)	(372,522)
Beginning Balance at Dec. 31, 2020	423,682	311,190	41,654	539,281	(95,921)	(372,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	12,865
Changes in fair market value of derivatives, net of tax	392
Changes in unrealized pension cost, net of tax	18,446
Cumulative translation adjustment, net of tax	13
Ending Balance at Jun. 30, 2021	454,309	314,341	40,007	549,553	(77,070)	(372,522)
Beginning Balance at Mar. 31, 2021	435,716	313,008	39,616	549,977	(94,363)	(372,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	875			875
Changes in fair market value of derivatives, net of tax	268				268
Changes in unrealized pension cost, net of tax	17,024				17,024
Cumulative translation adjustment, net of tax	1				1
Cash dividends	(1,299)			(1,299)
Issued shares on vesting of restricted stock units	(80)	1,333	(1,413)
Stock compensation	1,804		1,804
Ending Balance at Jun. 30, 2021	$ 454,309	$ 314,341	$ 40,007	$ 549,553	$ (77,070)	$ (372,522)