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 Income (Loss) [Member]	Total	Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Additional Paid-In Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Earnings Reinvested in the Business [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Treasury Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2019	$ 5,396	$ 98,425	$ 1,536,100	$ (595,324)	$ (163,008)	$ 881,589
Beginning balance (ASU 2016-13 [Member]) at Dec. 31, 2019							$ 0	$ 0	$ (853)	$ 0	$ 0	$ (853)
Beginning balance (in shares) at Dec. 31, 2019				11,682,636
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	84,303	$ 0	0	84,303
Other comprehensive Income (loss)	0	0	0	0	(23,394)	(23,394)
Cash dividends paid	0	0	(49,537)	0	0	(49,537)
Share-based compensation	0	4,017	0	0	0	4,017
Non-vested stock issued upon vesting	0	(1,352)	0	$ 1,352	0	0
Non-vested stock issued upon vesting (in shares)				(26,515)
Benefit plans	0	241	0	$ 833	0	1,074
Benefit plans (in shares)				(16,344)
Other	0	(13)	0	$ (401)	0	(414)
Other (in shares)				7,850
Ending balance at Sep. 30, 2020	5,396	101,318	1,570,013	$ (593,540)	(186,402)	896,785
Ending balance (in shares) at Sep. 30, 2020				11,647,627
Beginning balance at Jun. 30, 2020	5,396	99,962	1,553,622	$ (593,540)	(204,724)	860,716
Beginning balance (in shares) at Jun. 30, 2020				11,647,627
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	32,910	$ 0	0	32,910
Other comprehensive Income (loss)	0	0	0	0	18,322	18,322
Cash dividends paid	0	0	(16,519)	0	0	(16,519)
Share-based compensation	0	1,355	0	0	0	1,355
Other	0	1	0	$ 0	0	1
Other (in shares)				0
Ending balance at Sep. 30, 2020	5,396	101,318	1,570,013	$ (593,540)	(186,402)	896,785
Ending balance (in shares) at Sep. 30, 2020				11,647,627
Beginning balance at Dec. 31, 2020	5,396	102,909	1,578,662	$ (593,540)	(159,091)	934,336
Beginning balance (in shares) at Dec. 31, 2020				11,647,627
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	91,516	$ 0	0	91,516
Other comprehensive Income (loss)	0	0	0	0	(12,062)	(12,062)
Cash dividends paid	0	0	(49,468)	0	0	(49,468)
Share-based compensation	0	6,431	0	0	0	6,431
Non-vested stock issued upon vesting	0	(1,264)	0	$ 1,264	0	0
Non-vested stock issued upon vesting (in shares)				(24,711)
Benefit plans	0	338	0	$ 756	0	1,094
Benefit plans (in shares)				(14,791)
Purchase of treasury stock	0	0	0	$ (31,874)	0	(31,874)
Purchase of treasury stock (in shares)				382,593
Other	0	(204)	0	$ (377)	0	(581)
Other (in shares)				7,379
Ending balance at Sep. 30, 2021	5,396	108,210	1,620,710	$ (623,771)	(171,153)	939,392
Ending balance (in shares) at Sep. 30, 2021				11,998,097
Beginning balance at Jun. 30, 2021	5,396	105,967	1,603,239	$ (614,404)	(155,921)	944,277
Beginning balance (in shares) at Jun. 30, 2021				11,892,497
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	33,912	$ 0	0	33,912
Other comprehensive Income (loss)	0	0	0	0	(15,232)	(15,232)
Cash dividends paid	0	0	(16,441)	0	0	(16,441)
Share-based compensation	0	2,243	0	0	0	2,243
Purchase of treasury stock	0	0	0	$ (9,367)	0	(9,367)
Purchase of treasury stock (in shares)				105,600
Ending balance at Sep. 30, 2021	$ 5,396	$ 108,210	$ 1,620,710	$ (623,771)	$ (171,153)	$ 939,392
Ending balance (in shares) at Sep. 30, 2021				11,998,097