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	51,393	$ 0	0	51,393
Other comprehensive Income (loss)	0	0	0	0	(41,716)	(41,716)
Cash dividends paid	0	0	(33,018)	0	0	(33,018)
Share-based compensation	0	2,662	0	0	0	2,662
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	(14)	0	$ (401)	0	(415)
Other (in shares)				7,850
Ending balance at Jun. 30, 2020	5,396	99,962	1,553,622	$ (593,540)	(204,724)	860,716
Ending balance (in shares) at Jun. 30, 2020				11,647,627
Beginning balance at Mar. 31, 2020	5,396	99,080	1,539,520	$ (593,977)	(207,361)	842,658
Beginning balance (in shares) at Mar. 31, 2020				11,656,206
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	30,620	$ 0	0	30,620
Other comprehensive Income (loss)	0	0	0	0	2,637	2,637
Cash dividends paid	0	0	(16,518)	0	0	(16,518)
Share-based compensation	0	1,485	0	0	0	1,485
Non-vested stock issued upon vesting	0	(628)	0	$ 628	0	0
Non-vested stock issued upon vesting (in shares)				(12,315)
Other	0	25	0	$ (191)	0	(166)
Other (in shares)				3,736
Ending balance at Jun. 30, 2020	5,396	99,962	1,553,622	$ (593,540)	(204,724)	860,716
Ending balance (in shares) at Jun. 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	57,604	$ 0	0	57,604
Other comprehensive Income (loss)	0	0	0	0	3,170	3,170
Cash dividends paid	0	0	(33,027)	0	0	(33,027)
Share-based compensation	0	4,188	0	0	0	4,188
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	$ (22,507)	0	(22,507)
Purchase of treasury stock (in shares)				276,993
Other	0	(204)	0	$ (377)	0	(581)
Other (in shares)				7,379
Ending balance at Jun. 30, 2021	5,396	105,967	1,603,239	$ (614,404)	(155,921)	944,277
Ending balance (in shares) at Jun. 30, 2021				11,892,497
Beginning balance at Mar. 31, 2021	5,396	104,725	1,593,795	$ (604,040)	(174,230)	925,646
Beginning balance (in shares) at Mar. 31, 2021				11,776,654
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	25,936	$ 0	0	25,936
Other comprehensive Income (loss)	0	0	0	0	18,309	18,309
Cash dividends paid	0	0	(16,492)	0	0	(16,492)
Share-based compensation	0	2,075	0	0	0	2,075
Non-vested stock issued upon vesting	0	(701)	0	$ 701	0	0
Non-vested stock issued upon vesting (in shares)				(13,666)
Purchase of treasury stock	0	0	0	$ (10,842)	0	(10,842)
Purchase of treasury stock (in shares)				125,150
Other	0	(132)	0	$ (223)	0	(355)
Other (in shares)				4,359
Ending balance at Jun. 30, 2021	$ 5,396	$ 105,967	$ 1,603,239	$ (614,404)	$ (155,921)	$ 944,277
Ending balance (in shares) at Jun. 30, 2021				11,892,497