Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2018	$ 600,764	$ 47,619	$ 169,555	$ 485,967	$ (87,895)	$ (14,482)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income available to common shareholders	21,619			21,619
Other comprehensive income, net of tax	8,631					8,631
Cash dividends declared	(8,739)			(8,739)
Stock-based compensation expense	803		803
Restricted awards granted	0		(224)		224
Exercise of stock options	252		81		171
Purchase of treasury shares	(4,089)				(4,089)
Ending balance at Mar. 31, 2019	619,241	47,619	170,215	498,847	(91,589)	(5,851)
Beginning Balance at Dec. 31, 2019	657,983	47,619	170,309	539,253	(105,038)	5,840
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement Or Change In Accounting Principle, Effect Of Adoption, Quantification	(2,335)			(2,335)
Net income available to common shareholders	29,000			29,000
Other comprehensive income, net of tax	21,620					21,620
Cash dividends declared	(9,200)			(9,200)
Stock-based compensation expense	1,009		1,009
Restricted awards granted	0		(1,154)		1,154
Exercise of stock options	122		(68)		190
Purchase of treasury shares	(12,971)				(12,971)
Ending balance at Mar. 31, 2020	$ 685,228	$ 47,619	$ 170,096	$ 556,718	$ (116,665)	$ 27,460