Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Capital Stock [Member]	Surplus [Member]	Undivided Profits [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2017	$ 99,998	$ 175,651	$ 219,436	$ (1,806)	$ (34,971)	$ 458,308
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	14,808	0	0	14,808
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect	0	0	1,346	(1,346)	0	0
Other comprehensive income (loss), net of tax	0	0	0	(5,338)	0	(5,338)
Cash dividend declared	0	0	(6,323)	0	0	(6,323)
Stock options exercised	4	16	0	0	0	20
Sale of treasury stock	0	(21)	0	0	615	594
Stock based compensation expense	0	28	0	0	0	28
Balance at Mar. 31, 2018	100,002	175,674	229,267	(8,490)	(34,356)	462,097
Balance at Dec. 31, 2017	99,998	175,651	219,436	(1,806)	(34,971)	458,308
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income						30,213
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect				(1,346)
Other comprehensive income (loss), net of tax						(6,644)
Balance at Jun. 30, 2018	100,093	176,243	238,342	(9,796)	(34,067)	470,815
Balance at Mar. 31, 2018	100,002	175,674	229,267	(8,490)	(34,356)	462,097
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	15,405	0	0	15,405
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect	0	0	0	0	0	0
Other comprehensive income (loss), net of tax	0	0	0	(1,306)	0	(1,306)
Cash dividend declared	0	0	(6,330)	0	0	(6,330)
Stock options exercised	91	592	0	0	0	683
Purchase of treasury stock	0	0	0	0	(379)	(379)
Sale of treasury stock	0	(72)	0	0	668	596
Stock based compensation expense	0	49	0	0	0	49
Balance at Jun. 30, 2018	100,093	176,243	238,342	(9,796)	(34,067)	470,815
Balance at Dec. 31, 2018	100,175	176,710	256,397	(10,309)	(33,102)	489,871
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	14,558	0	0	14,558
Other comprehensive income (loss), net of tax	0	0	0	3,298	0	3,298
Cash dividend declared	0	0	(6,591)	0	0	(6,591)
Stock options exercised	5	30	0	0	0	35
Purchase of treasury stock	0	0	0	0	(35)	(35)
Sale of treasury stock	0	(218)	0	0	812	594
Stock based compensation expense	0	(12)	0	0	0	(12)
Balance at Mar. 31, 2019	100,180	176,510	264,364	(7,011)	(32,325)	501,718
Balance at Dec. 31, 2018	100,175	176,710	256,397	(10,309)	(33,102)	489,871
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income						29,225
Other comprehensive income (loss), net of tax						8,535
Balance at Jun. 30, 2019	100,180	176,396	272,433	(1,774)	(31,605)	515,630
Balance at Mar. 31, 2019	100,180	176,510	264,364	(7,011)	(32,325)	501,718
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	14,667	0	0	14,667
Other comprehensive income (loss), net of tax	0	0	0	5,237	0	5,237
Cash dividend declared	0	0	(6,598)	0	0	(6,598)
Sale of treasury stock	0	(120)	0	0	720	600
Stock based compensation expense	0	6	0	0	0	6
Balance at Jun. 30, 2019	$ 100,180	$ 176,396	$ 272,433	$ (1,774)	$ (31,605)	$ 515,630