Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock at $1 par value	[1]	Capital in excess of par value	Reinvested earnings	Reinvested earnings Cumulative Effect, Period of Adoption, Adjustment	Employee benefit stock	Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) Cumulative Effect, Period of Adoption, Adjustment	Treasury stock
Balance at beginning of period at Dec. 31, 2017	$ 277,452		$ 37,165		$ 32,182	$ 244,224		$ (460)	$ (10,893)		$ (24,766)
Balance at beginning of period (Accounting Standards Update 2014-09) at Dec. 31, 2017		$ (128)					$ (128)
Balance at beginning of period (Accounting Standards Update 2018-02) at Dec. 31, 2017							$ 1,700			$ (1,700)
Net earnings	27,790					27,790
Pension and postretirement benefits (net of tax effect)	13,657								13,657
Foreign currency translation	(484)								(484)
Cash dividends	(16,273)					(16,273)
Stock options exercised	1,511		33		1,410						68
ESSOP transactions	76				(78)			154
Stock-based compensation	4,174				4,174
Purchase of common stock for treasury stock	(4,795)										(4,795)
Issuance of treasury stock	523				394						129
Balance at end of period at Dec. 31, 2018	303,503		37,198		38,082	257,313		(306)	580		(29,364)
Net earnings	47,177					47,177
Pension and postretirement benefits (net of tax effect)	(97)								(97)
Foreign currency translation	(58)								(58)
Cash dividends	(18,611)					(18,611)
Stock options exercised	1,961		2		1,708						251
ESSOP transactions	553				401			152
Stock-based compensation	1,214				1,214
Purchase of common stock for treasury stock	(5,207)										(5,207)
Issuance of treasury stock	633				551						82
Balance at end of period at Dec. 31, 2019	331,068		37,200		41,956	285,879		(154)	425		(34,238)
Net earnings	49,343					49,343
Pension and postretirement benefits (net of tax effect)	(208)								(208)
Foreign currency translation	1,096								1,096
Cash dividends	(20,372)					(20,372)
Stock options exercised	1,058		21		877						160
ESSOP transactions	434				280			$ 154
Stock-based compensation	1,415				1,415
Purchase of common stock for treasury stock	(3,116)										(3,116)
Issuance of treasury stock	541				436						105
Balance at end of period at Dec. 31, 2020	$ 361,259		$ 37,221		$ 44,964	$ 314,850			$ 1,313		$ (37,089)

[1] Each common share of stock equals $1 par value; therefore, the number of common shares is the same as the dollar value.