CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total
Balance 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	33,498	0	0	33,498
Other comprehensive income, net of tax	0	0	0	5,541	0	5,541
Cash dividends paid	0	0	(8,674)	0	0	(8,674)
Purchase of treasury stock	0	0	0	0	(5,333)	(5,333)
Stock-based compensation	0	3,319	0	0	686	4,005
Employee Stock Ownership Plan	0	1,014	0	0	1,145	2,159
Balance at Jun. 30, 2017	47,872	101,183	361,288	(5,487)	(32,632)	472,224
Balance at Mar. 31, 2017				(8,340)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings						17,764
Other comprehensive income, net of tax						2,853
Balance at Jun. 30, 2017	$ 47,872	$ 101,183	$ 361,288	$ (5,487)	$ (32,632)	$ 472,224