Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2020	$ 701,106	$ 47,619	$ 171,304	$ 589,988	$ (139,038)	$ 31,233
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,694			64,694
Other comprehensive income (loss)	(16,016)					(16,016)
Cash dividends declared	(27,219)			(27,219)
Stock-based compensation expense	2,430		2,430
Restricted awards granted	0		(1,860)		1,860
Exercise of stock options	622		(1,574)		2,196
Purchase of treasury shares	(48,321)				(48,321)
Ending balance at Sep. 30, 2021	$ 677,296	47,619	170,300	627,463	(183,303)	15,217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	13,098
Beginning Balance at Jun. 30, 2021	$ 695,476	47,619	169,674	613,553	(157,936)	22,566
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,732			22,732
Other comprehensive income (loss)	(7,349)					(7,349)
Cash dividends declared	(8,822)			(8,822)
Stock-based compensation expense	652		652
Restricted awards granted	0		0		0
Exercise of stock options	85		(26)		111
Purchase of treasury shares	(25,478)				(25,478)
Ending balance at Sep. 30, 2021	$ 677,296	47,619	170,300	627,463	(183,303)	15,217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,408
Beginning Balance at Dec. 31, 2021	$ 681,105	47,619	170,942	641,826	(193,542)	14,260
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	71,408			71,408
Other comprehensive income (loss)	(159,742)					(159,742)
Cash dividends declared	(27,577)			(27,577)
Stock-based compensation expense	2,412		2,412
Restricted awards granted	0		(2,821)		2,821
Exercise of stock options	697		(395)		1,092
Purchase of treasury shares	(20,015)				(20,015)
Ending balance at Sep. 30, 2022	$ 548,288	47,619	170,138	685,657	(209,644)	(145,482)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	13,634
Beginning Balance at Jun. 30, 2022	$ 591,993	47,619	169,557	667,933	(209,133)	(83,983)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27,374			27,374
Other comprehensive income (loss)	(61,499)					(61,499)
Cash dividends declared	(9,650)			(9,650)
Stock-based compensation expense	754		754
Restricted awards granted	0		(163)		163
Exercise of stock options	36		(10)		46
Purchase of treasury shares	(720)				(720)
Ending balance at Sep. 30, 2022	$ 548,288	$ 47,619	$ 170,138	$ 685,657	$ (209,644)	$ (145,482)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	556