Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Total
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, net of tax	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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared (in dollars per share)	$ 1.06
Exercise of stock options (in shares)	8,140
Purchase of treasury shares (in shares)	161,950
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, net of tax	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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared (in dollars per share)	$ 0.53
Exercise of stock options (in shares)	2,502
Purchase of treasury shares (in shares)	107,210
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]
Impact of adopting CECL	(2,335)			(2,335)
Net income available to common shareholders	47,249			47,249
Other comprehensive income, net of tax	25,189					25,189
Cash dividends declared	(18,363)			(18,363)
Stock-based compensation expense	1,702		1,702
Restricted awards granted	0		(2,033)		2,033
Exercise of stock options	189		(97)		286
Purchase of treasury shares	(17,864)				(17,864)
Ending balance at Jun. 30, 2020	$ 693,750	47,619	169,881	565,804	(120,583)	31,029
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared (in dollars per share)	$ 1.14
Exercise of stock options (in shares)	4,166
Purchase of treasury shares (in shares)	261,137
Beginning Balance at Mar. 31, 2020	$ 685,228	47,619	170,096	556,718	(116,665)	27,460
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income available to common shareholders	18,251			18,251
Other comprehensive income, net of tax	3,569					3,569
Cash dividends declared	(9,165)			(9,165)
Stock-based compensation expense	693		693
Restricted awards granted	0		(879)		879
Exercise of stock options	67		(29)		96
Purchase of treasury shares	(4,893)				(4,893)
Ending balance at Jun. 30, 2020	$ 693,750	$ 47,619	$ 169,881	$ 565,804	$ (120,583)	$ 31,029
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared (in dollars per share)	$ 0.57
Exercise of stock options (in shares)	1,516
Purchase of treasury shares (in shares)	79,238