CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Earnings Reinvested in the Business [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Beginning balance at Dec. 31, 2017	$ 5,396	$ 107,176	$ 1,414,485	$ (525,422)	$ (149,334)	$ 852,301
Beginning balance (in shares) at Dec. 31, 2017				10,759,291
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	77,317	$ 0	0	77,317
Other comprehensive income (loss)	0	0	0	0	(12,782)	(12,782)
Cash dividends paid	0	0	(28,244)	0	0	(28,244)
Share-based compensation	0	1,783	0	0	0	1,783
Stock options exercised	0	(80)	0	$ 200	0	120
Stock options exercised (in shares)				(4,000)
Non-vested stock issued upon vesting	0	(5,454)	0	$ 5,454	0	0
Non-vested stock issued upon vesting (in shares)				(111,185)
Benefit plans	0	350	0	$ 769	0	1,119
Benefit plans (in shares)				(15,126)
Purchase of treasury stock	0	0	0	$ (72,704)	0	(72,704)
Purchase of treasury stock (in shares)				1,000,000
Other	0	(832)	418	$ (2,067)	0	(2,481)
Other (in shares)				42,243
Ending balance at Jun. 30, 2018	5,396	102,943	1,463,976	$ (593,770)	(162,116)	816,429
Ending balance (in shares) at Jun. 30, 2018				11,671,223
Beginning balance at Mar. 31, 2018	5,396	103,099	1,438,823	$ (594,392)	(125,470)	827,456
Beginning balance (in shares) at Mar. 31, 2018				11,683,443
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	39,123	$ 0	0	39,123
Other comprehensive income (loss)	0	0	0	0	(36,646)	(36,646)
Cash dividends paid	0	0	(13,970)	0	0	(13,970)
Share-based compensation	0	529	0	0	0	529
Stock options exercised	0	(42)	0	$ 102	0	60
Stock options exercised (in shares)				(2,000)
Non-vested stock issued upon vesting	0	(612)	0	$ 612	0	0
Non-vested stock issued upon vesting (in shares)				(12,033)
Other	0	(31)	0	$ (92)	0	(123)
Other (in shares)				1,813
Ending balance at Jun. 30, 2018	5,396	102,943	1,463,976	$ (593,770)	(162,116)	816,429
Ending balance (in shares) at Jun. 30, 2018				11,671,223
Beginning balance at Dec. 31, 2018	5,396	101,663	1,516,243	$ (597,800)	(165,555)	859,947
Beginning balance (in shares) at Dec. 31, 2018				11,731,223
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	67,138	$ 0	0	67,138
Other comprehensive income (loss)	0	0	0	0	2,012	2,012
Cash dividends paid	0	0	(30,453)	0	0	(30,453)
Share-based compensation	0	(1,155)	0	0	0	(1,155)
Non-vested stock issued upon vesting	0	(2,331)	0	$ 2,331	0	0
Non-vested stock issued upon vesting (in shares)				(45,741)
Benefit plans	0	72	0	$ 948	0	1,020
Benefit plans (in shares)				(18,597)
Other	0	(212)	0	$ (815)	0	(1,027)
Other (in shares)				15,991
Ending balance at Jun. 30, 2019	5,396	98,037	1,552,928	$ (595,336)	(163,543)	897,482
Ending balance (in shares) at Jun. 30, 2019				11,682,876
Beginning balance at Mar. 31, 2019	5,396	100,485	1,533,832	$ (595,718)	(166,271)	877,724
Beginning balance (in shares) at Mar. 31, 2019				11,690,379
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	34,331	$ 0	0	34,331
Other comprehensive income (loss)	0	0	0	0	2,728	2,728
Cash dividends paid	0	0	(15,235)	0	0	(15,235)
Share-based compensation	0	(1,842)	0	0	0	(1,842)
Non-vested stock issued upon vesting	0	(547)	0	$ 547	0	0
Non-vested stock issued upon vesting (in shares)				(10,725)
Other	0	(59)	0	$ (165)	0	(224)
Other (in shares)				3,222
Ending balance at Jun. 30, 2019	$ 5,396	$ 98,037	$ 1,552,928	$ (595,336)	$ (163,543)	$ 897,482
Ending balance (in shares) at Jun. 30, 2019				11,682,876