Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock	Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Retained Earnings	Deferred Compensation	Treasury Stock at Cost	Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2012	$ 65,455	$ 202,535	$ 143,170	$ 778,202	$ 11,106	$ (404,105)	$ 796,363
Balance (in shares) at Dec. 31, 2012	42,525,248
Increase (Decrease) in Shareholders' Equity
Net earnings				126,255			126,255
Other comprehensive earnings (loss), net of tax			(7,143)				(7,143)
Deferred compensation under Rabbi trust plans					456	(456)
Stock option excess tax benefit		6,310					6,310
Exercise of stock options	$ 458	(140)					318
Exercise of stock options (in shares)	457,176
Dividends paid ($2.75, $3.71 and $2.17 per share during 2015, 2014 and 2013, respectively)				(93,137)			(93,137)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2013	$ 65,913	208,705	136,027	811,320	11,562	(404,561)	828,966
Balance (in shares) at Dec. 31, 2013	42,982,424
Increase (Decrease) in Shareholders' Equity
Net earnings				135,445			135,445
Other comprehensive earnings (loss), net of tax			35,356				35,356
Deferred compensation under Rabbi trust plans					2,207	(2,207)
Stock option excess tax benefit		1,766					1,766
Exercise of stock options	$ 120	3,266					3,386
Exercise of stock options (in shares)	120,291
Dividends paid ($2.75, $3.71 and $2.17 per share during 2015, 2014 and 2013, respectively)				(159,857)			(159,857)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2014	$ 66,033	213,737	171,383	786,908	13,769	(406,768)	845,062
Balance (in shares) at Dec. 31, 2014	43,102,715
Increase (Decrease) in Shareholders' Equity
Net earnings				137,544			137,544
Other comprehensive earnings (loss), net of tax			(47,609)				(47,609)
Deferred compensation under Rabbi trust plans					(3,122)	3,122
Stock option excess tax benefit		11,413					11,413
Exercise of stock options	$ 441	(3,805)					(3,364)
Exercise of stock options (in shares)	441,413
Dividends paid ($2.75, $3.71 and $2.17 per share during 2015, 2014 and 2013, respectively)				(119,577)			(119,577)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2015	$ 66,474	$ 221,345	$ 123,774	$ 804,875	$ 10,647	$ (403,646)	$ 823,469
Balance (in shares) at Dec. 31, 2015	43,544,128