CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Common Stock [Member] Adjustments Due to Adoption of ASU 2014-09 [Member]	Capital In Excess of Par Value [Member]	Capital In Excess of Par Value [Member] Adjustments Due to Adoption of ASU 2014-09 [Member]	Retained Earnings [Member]	Retained Earnings [Member] Adjustments Due to Adoption of ASU 2014-09 [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Other Comprehensive Income [Member] Adjustments Due to Adoption of ASU 2014-09 [Member]	Treasury Stock [Member]	Treasury Stock [Member] Adjustments Due to Adoption of ASU 2014-09 [Member]	Total	Adjustments Due to Adoption of ASU 2014-09 [Member]
Balance at beginning of period at Dec. 31, 2016	$ 47,872		$ 96,850		$ 336,464		$ (11,028)		$ (29,130)		$ 441,028
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0		0		37,976		0		0		37,976
Other comprehensive income (loss), net of tax	0		0		0		6,919		0		6,919
Cash dividends paid	0		0		(17,287)		0		0		(17,287)
Purchase of treasury stock	0		0		0		0		(24,779)		(24,779)
Stock-based compensation	0		2,193		0		0		5,445		7,638
Employee stock ownership plan	0		1,014		0		0				2,159
Employee stock ownership plan									1,145
Balance at beginning of period at Dec. 31, 2017	47,872		100,057		357,153		(4,109)		(47,319)		453,654
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0		0		43,003		0		0		43,003
Other comprehensive income (loss), net of tax	0		0		0		(5,485)		0		(5,485)
Cash dividends paid	0		0		(18,854)		0		0		(18,854)
Purchase of treasury stock	0		0		0		0		(14,483)		(14,483)
Stock-based compensation	0		1,648		0		0		6,350		7,998
Employee stock ownership plan	0		765		0		0				2,557
Employee stock ownership plan									1,792
Balance at beginning of period at Dec. 31, 2018	47,872		102,470		380,113		(9,594)		(53,660)		467,201
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment | ASC 606 [Member]		$ 0		$ 0		$ (1,189)		$ 0		$ 0		$ (1,189)
Net earnings	0		0		57,917		0		0		57,917
Other comprehensive income (loss), net of tax	0		0		0		1,005		0		1,005
Cash dividends paid	0		0		(20,593)		0		0		(20,593)
Purchase of treasury stock	0		0		0		0		(10,738)		(10,738)
Stock-based compensation	0		(473)		0		0		7,390		6,917
Employee stock ownership plan	0		745		0		0				2,519
Employee stock ownership plan									1,774
Balance at beginning of period at Dec. 31, 2019	$ 47,872		$ 102,742		$ 417,437		$ (8,589)		$ (55,234)		$ 504,228