Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Capital Surplus	Capital Surplus Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock	Treasury Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income Cumulative Effect, Period of Adoption, Adjusted Balance
Beginning Balance at Dec. 31, 2019	$ 657,983	$ (2,335)	$ 655,648	$ 47,619	$ 47,619	$ 170,309	$ 170,309	$ 539,253	$ (2,335)	$ 536,918	$ (105,038)	$ (105,038)	$ 5,840	$ 5,840
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-13 [Member]
Ending balance at Jun. 30, 2020	$ 693,750			47,619		169,881		565,804			(120,583)		31,029
Beginning Balance at Dec. 31, 2019	657,983	$ (2,335)	$ 655,648	47,619	$ 47,619	170,309	$ 170,309	539,253	$ (2,335)	$ 536,918	(105,038)	$ (105,038)	5,840	$ 5,840
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	67,374							67,374
Other comprehensive income (loss)	24,650												24,650
Cash dividends declared	(27,391)							(27,391)
Stock-based compensation expense	2,455					2,455
Restricted awards granted	0					(2,126)					2,126
Exercise of stock options	223					(112)					335
Purchase of treasury shares	(31,600)										(31,600)
Ending balance at Sep. 30, 2020	691,359			47,619		170,526		576,901			(134,177)		30,490
Beginning Balance at Jun. 30, 2020	693,750			47,619		169,881		565,804			(120,583)		31,029
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,126							20,126
Other comprehensive income (loss)	(539)												(539)
Cash dividends declared	(9,029)							(9,029)
Stock-based compensation expense	753					753
Restricted awards granted	0					(93)					93
Exercise of stock options	34					(15)					49
Purchase of treasury shares	(13,736)										(13,736)
Ending balance at Sep. 30, 2020	691,359			47,619		170,526		576,901			(134,177)		30,490
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
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