CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Earnings Reinvested in the Business [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Total
Beginning balance at Dec. 31, 2014	$ 5,396	$ 110,969	$ 1,243,627	$ (227,929)	$ (85,128)
Beginning Balance (in shares) at Dec. 31, 2014				6,529,891
Net earnings			106,785			$ 106,785
Other comprehensive income					(84,934)
Cash dividends paid			(48,110)
Share-based compensation		1,598
Stock options exercised		(356)		$ 788
Stock options exercised (in shares)				(21,000)
Non-vested stock issued upon vesting		(3,080)		$ 3,080
Non-vested stock issued upon vesting (in shares)				(74,300)
Benefit plans		416		$ 546
Benefit plans (in shares)				(15,165)
Purchase of treasury stock				$ (178,037)
Purchase of treasury stock (in shares)				2,733,301
Other		427		$ (931)
Other (in shares)				22,116
Ending balance at Dec. 31, 2015	5,396	109,974	1,302,302	$ (402,483)	(170,062)
Ending Balance (in shares) at Dec. 31, 2015				9,174,843
Net earnings			126,256			126,256
Other comprehensive income					(43,403)
Cash dividends paid			(49,635)
Share-based compensation		7,709
Stock options exercised		(650)		$ 1,354
Stock options exercised (in shares)				(30,500)
Non-vested stock issued upon vesting		(7,769)		$ 7,769
Non-vested stock issued upon vesting (in shares)				(172,147)
Benefit plans		229		$ 698
Benefit plans (in shares)				(15,839)
Purchase of treasury stock				$ (47,534)
Purchase of treasury stock (in shares)				702,698
Other		(1,807)		$ (2,603)
Other (in shares)				57,449
Ending balance at Dec. 31, 2016	5,396	107,686	1,378,923	$ (442,799)	(213,465)	835,741
Ending Balance (in shares) at Dec. 31, 2016				9,716,504
Net earnings			89,600			89,600
Other comprehensive income					64,131
Cash dividends paid			(54,038)
Share-based compensation		5,855
Stock options exercised		(202)		$ 499
Stock options exercised (in shares)				(10,667)
Non-vested stock issued upon vesting		(5,478)		$ 5,478
Non-vested stock issued upon vesting (in shares)				(114,393)
Benefit plans		445		$ 596
Benefit plans (in shares)				(12,999)
Purchase of treasury stock				$ (87,217)
Purchase of treasury stock (in shares)				1,139,734
Other		(1,130)		$ (1,979)
Other (in shares)				41,112
Ending balance at Dec. 31, 2017	$ 5,396	$ 107,176	$ 1,414,485	$ (525,422)	$ (149,334)	$ 852,301
Ending Balance (in shares) at Dec. 31, 2017				10,759,291