CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Common Stock [Member]	Capital In Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2011	$ 47,872	$ 79,789	$ 153,555	$ 3,299	$ (12,562)	$ 271,953
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	41,353	0	0	41,353
Other comprehensive income, net of tax	0	0	0	580	0	580
Cash dividends paid	0	0	(8,215)	0	0	(8,215)
Purchase of treasury stock	0	0	0	0	(4,999)	(4,999)
Stock-based compensation and related tax benefits	0	584	0	0	2,010	2,594
Stock options exercised and related tax benefits	0	136	0	0	320	456
Employee Stock Ownership Plan	0	1,839	0	0	2,026	3,865
Balance at Dec. 31, 2012	47,872	82,348	186,693	3,879	(13,205)	307,587
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	51,450	0	0	51,450
Other comprehensive income, net of tax	0	0	0	(2,093)	0	(2,093)
Cash dividends paid	0	0	(10,107)	0	0	(10,107)
Purchase of treasury stock	0	0	0	0	(6,864)	(6,864)
Stock-based compensation and related tax benefits	0	2,917	0	0	1,933	4,850
Stock options exercised and related tax benefits	0	84	0	0	149	233
Employee Stock Ownership Plan	0	2,214	0	0	2,162	4,376
Balance at Dec. 31, 2013	47,872	87,563	228,036	1,786	(15,825)	349,432
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	43,029	0	0	43,029
Other comprehensive income, net of tax	0	0	0	(4,438)	0	(4,438)
Cash dividends paid	0	0	(11,905)	0	0	(11,905)
Purchase of treasury stock	0	0	0	0	(10,000)	(10,000)
Stock-based compensation and related tax benefits	0	3,005	0	0	3,065	6,070
Stock options exercised and related tax benefits	0	17	0	0	122	139
Employee Stock Ownership Plan	0	826	0	0	1,000	1,826
Balance at Dec. 31, 2014	$ 47,872	$ 91,411	$ 259,160	$ (2,652)	$ (21,638)	$ 374,153