Condensed Consolidated Statement of Shareholders' Equity Condensed Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated other comprehensive (loss) income	Treasury Stock
Beginning Balance at Dec. 31, 2017	$ 343,805	$ 304,777	$ 41,084	$ 420,160	$ (78,960)	$ (343,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	11,548			11,548
Changes in fair market value of derivatives, net of tax	807				807
Changes in unrealized pension cost, net of tax	1,107				1,107
Cumulative translation adjustment, net of tax	243				243
Cash Dividends	(1,320)			(1,320)
Issued shares on vesting of restricted stock units	(1,423)	945	(2,368)
Stock compensation	965		965
Ending Balance at Mar. 31, 2018	355,732	305,722	39,681	430,388	(76,803)	(343,256)
Beginning Balance at Dec. 31, 2017	343,805	304,777	41,084	420,160	(78,960)	(343,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	28,968
Changes in fair market value of derivatives, net of tax	1,498
Changes in unrealized pension cost, net of tax	3,513
Cumulative translation adjustment, net of tax	(131)
Ending Balance at Sep. 30, 2018	376,205	306,574	41,807	445,160	(74,080)	(343,256)
Beginning Balance at Mar. 31, 2018	355,732	305,722	39,681	430,388	(76,803)	(343,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	7,209			7,209
Changes in fair market value of derivatives, net of tax	67				67
Changes in unrealized pension cost, net of tax	1,249				1,249
Cumulative translation adjustment, net of tax	(375)				(375)
Cash Dividends	(1,323)			(1,323)
Issued shares on vesting of restricted stock units	(5)	848	(853)
Stock compensation	1,206		1,206
Ending Balance at Jun. 30, 2018	363,760	306,570	40,034	436,274	(75,862)	(343,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	10,211
Changes in fair market value of derivatives, net of tax	624				624
Changes in unrealized pension cost, net of tax	1,157				1,157
Cumulative translation adjustment, net of tax	1				1
Cash Dividends	1,325			(1,325)
Issued shares on vesting of restricted stock units	(4)	4	(8)
Stock compensation	1,781		1,781
Ending Balance at Sep. 30, 2018	376,205	306,574	41,807	445,160	(74,080)	(343,256)
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
Treasury Stock, Value, Acquired, Cost Method	(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)
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
Treasury Stock, Value, Acquired, Cost Method	(4,153)					(4,153)
Issued shares on vesting of restricted stock units	0	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
Treasury Stock, Value, Acquired, Cost Method	(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)