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	124,510	$ 0	0	124,510
Other comprehensive income (loss)	0	0	0	0	(12,014)	(12,014)
Cash dividends paid	0	0	(42,195)	0	0	(42,195)
Share-based compensation	0	1,541	0	0	0	1,541
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	$ (76,734)	0	(76,734)
Purchase of treasury stock (in shares)				1,060,000
Other	0	(830)	418	$ (2,067)	0	(2,479)
Other (in shares)				42,243
Ending balance at Sep. 30, 2018	5,396	102,703	1,497,218	$ (597,800)	(161,348)	846,169
Ending balance (in shares) at Sep. 30, 2018				11,731,223
Beginning balance at Jun. 30, 2018	5,396	102,943	1,463,976	$ (593,770)	(162,116)	816,429
Beginning balance (in shares) at Jun. 30, 2018				11,671,223
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	47,193	$ 0	0	47,193
Other comprehensive income (loss)	0	0	0	0	768	768
Cash dividends paid	0	0	(13,951)	0	0	(13,951)
Share-based compensation	0	(242)	0	0	0	(242)
Purchase of treasury stock	0	0	0	$ (4,030)	0	(4,030)
Purchase of treasury stock (in shares)				60,000
Other	0	2	0	$ 0	0	2
Other (in shares)				0
Ending balance at Sep. 30, 2018	5,396	102,703	1,497,218	$ (597,800)	(161,348)	846,169
Ending balance (in shares) at Sep. 30, 2018				11,731,223
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	99,009	$ 0	0	99,009
Other comprehensive income (loss)	0	0	0	0	(15,755)	(15,755)
Cash dividends paid	0	0	(45,688)	0	0	(45,688)
Share-based compensation	0	(816)	0	0	0	(816)
Non-vested stock issued upon vesting	0	(2,343)	0	$ 2,343	0	0
Non-vested stock issued upon vesting (in shares)				(45,981)
Benefit plans	0	72	0	$ 948	0	1,020
Benefit plans (in shares)				(18,597)
Other	0	(229)	0	$ (815)	0	(1,044)
Other (in shares)				15,991
Ending balance at Sep. 30, 2019	5,396	98,347	1,569,564	$ (595,324)	(181,310)	896,673
Ending balance (in shares) at Sep. 30, 2019				11,682,636
Beginning balance at Jun. 30, 2019	5,396	98,037	1,552,928	$ (595,336)	(163,543)	897,482
Beginning balance (in shares) at Jun. 30, 2019				11,682,876
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	31,871	$ 0	0	31,871
Other comprehensive income (loss)	0	0	0	0	(17,767)	(17,767)
Cash dividends paid	0	0	(15,235)	0	0	(15,235)
Share-based compensation	0	339	0	0	0	339
Non-vested stock issued upon vesting	0	(12)	0	$ 12	0	0
Non-vested stock issued upon vesting (in shares)				(240)
Other	0	(17)	0	$ 0	0	(17)
Other (in shares)				0
Ending balance at Sep. 30, 2019	$ 5,396	$ 98,347	$ 1,569,564	$ (595,324)	$ (181,310)	$ 896,673
Ending balance (in shares) at Sep. 30, 2019				11,682,636