Consolidated Statements of Changes in Shareholders' Equity 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, 2017	$ 502,507	$ 47,619	$ 140,960	$ 444,481	$ (124,909)	$ (5,644)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income available to common shareholders	38,590			38,590
Other comprehensive income (loss)	(10,650)					(10,650)
New Accounting Pronouncement	0					(2,657)
New Accounting Pronouncement | Accounting Standards Update 2016-01	(2,700)			2,657		(2,657)
Cash dividends declared	(14,213)			(14,213)
Stock-based compensation expense	1,242		1,242
Restricted awards granted	0		(1,494)		1,494
Exercise of stock options	968		(617)		1,585
Purchase of treasury shares	(14,690)				(14,690)
Ending balance at Jun. 30, 2018	503,754	47,619	140,091	471,515	(136,520)	(18,951)
Beginning Balance at Mar. 31, 2018	491,882	47,619	140,547	457,650	(137,420)	(16,514)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income available to common shareholders	20,979			20,979
Other comprehensive income (loss)	(2,437)					(2,437)
Cash dividends declared	(7,114)			(7,114)
Stock-based compensation expense	449		449
Restricted awards granted	0		(359)		359
Exercise of stock options	688		(546)		1,234
Purchase of treasury shares	(693)				(693)
Ending balance at Jun. 30, 2018	503,754	47,619	140,091	471,515	(136,520)	(18,951)
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	44,370			44,370
Other comprehensive income (loss)	19,570					19,570
Cash dividends declared	(17,426)			(17,426)
Stock-based compensation expense	1,374		1,374
Restricted awards granted	0		(1,557)		1,557
Exercise of stock options	365		2		363
Purchase of treasury shares	(12,109)				(12,109)
Ending balance at Jun. 30, 2019	636,908	47,619	169,374	512,911	(98,084)	5,088
Beginning Balance at Mar. 31, 2019	619,241	47,619	170,215	498,847	(91,589)	(5,851)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income available to common shareholders	22,751			22,751
Other comprehensive income (loss)	10,939					10,939
Cash dividends declared	(8,687)			(8,687)
Stock-based compensation expense	571		571
Restricted awards granted	0		(1,333)		1,333
Exercise of stock options	113		(79)		192
Purchase of treasury shares	(8,020)				(8,020)
Ending balance at Jun. 30, 2019	$ 636,908	$ 47,619	$ 169,374	$ 512,911	$ (98,084)	$ 5,088