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, 2015	$ 47,872		$ 93,247		$ 291,481		$ (6,474)		$ (34,147)		$ 391,979
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0		0		60,430		0		0		60,430
Other comprehensive income (loss), net of tax	0		0		0		(4,554)		0		(4,554)
Cash dividends paid	0		0		(15,447)		0		0		(15,447)
Purchase of treasury stock	0		0		0		0		(377)		(377)
Stock-based compensation and related tax benefits	0		3,148		0		0		3,828		6,976
Employee stock ownership plan	0		455		0		0		1,566		2,021
Balance at end 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 and related tax benefits	0		2,193		0		0		5,445		7,638
Employee stock ownership plan	0		1,014		0		0		1,145		2,159
Balance at end 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]
Cumulative effect adjustment (Note 1) | ASC 606 [Member]		$ 0		$ 0		$ (1,189)		$ 0		$ 0		$ (1,189)
Net earnings	0		0		43,003		0		0		43,003
Net earnings | ASC 606 [Member]												$ 52
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 and related tax benefits	0		1,648		0		0		6,350		7,998
Employee stock ownership plan	0		765		0		0		1,792		2,557
Balance at end of period at Dec. 31, 2018	$ 47,872		$ 102,470		$ 380,113		$ (9,594)		$ (53,660)		$ 467,201