Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period Of Adoption, Adjustment	Common Stock [Member]	Common Stock [Member] Cumulative Effect, Period Of Adoption, Adjustment	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Cumulative Effect, Period Of Adoption, Adjustment	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period Of Adoption, Adjustment	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Other Comprehensive (Loss) Income [Member] Cumulative Effect, Period Of Adoption, Adjustment		Treasury Stock [Member]	Treasury Stock [Member] Cumulative Effect, Period Of Adoption, Adjustment
Beginning balance at Dec. 31, 2018	$ 624,133		$ 157,784		$ 292,401		$ 248,167		$ (28,416)			$ (45,803)
Beginning balance (Accounting Standards Update 2016-02) at Dec. 31, 2018		$ (1,525)						$ (1,525)
Beginning balance (Accounting Standards Update 2017-12) at Dec. 31, 2018		0						(83)		$ 83
Beginning balance (Accounting Standards Update 2017-08) at Dec. 31, 2018		(39)						(39)
Beginning balance, shares at Dec. 31, 2018			29,270,852
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,547		$ 0		0		32,547		0			0
Other comprehensive income, net of income tax	6,384		0		0		0		6,384			0
Cash dividends declared	(11,711)		0		0		(11,711)		0			0
Stock-based compensation	1,230		0		1,230		0		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	1,135		$ 0		77		1		0			1,057
Stock issued under dividend reinvestment and employee stock purchase plans, shares			48,183
Exercise of stock options	691		$ 0		(102)		0		0			793
Exercise of stock options, shares			39,500
Cancellations of performance-based restricted stock awards	0		$ 0		341		0		0			(341)
Cancellation of performance-based restricted stock awards, shares			(17,349)
Purchases of treasury stock	(1,175)		$ 0		0		0		0			(1,175)
Purchases of treasury stock, shares			(46,244)
Ending balance at Jun. 30, 2019	$ 651,670		$ 157,784		293,947		267,357		(21,949)			(45,469)
Ending balance, shares at Jun. 30, 2019			29,294,942
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.40
Beginning balance at Mar. 31, 2019	$ 637,606		$ 157,784		293,255		256,746		(24,238)			(45,941)
Beginning balance, shares at Mar. 31, 2019			29,272,502
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,468		$ 0		0		16,468		0			0
Other comprehensive income, net of income tax	2,289		0		0		0		2,289			0
Cash dividends declared	(5,858)		0		0		(5,858)		0			0
Stock-based compensation	656		0		656		0		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	564		$ 0		47		1		0			516
Stock issued under dividend reinvestment and employee stock purchase plans, shares			22,440
Exercise of stock options	170		$ 0		(11)		0		0			181
Exercise of stock options, shares			9,000
Purchases of treasury stock	(225)		$ 0		0		0		0			(225)
Purchases of treasury stock, shares			(9,000)
Ending balance at Jun. 30, 2019	$ 651,670		$ 157,784		293,947		267,357		(21,949)			(45,469)
Ending balance, shares at Jun. 30, 2019			29,294,942
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.20
Beginning balance at Dec. 31, 2019	$ 675,122		$ 157,784		294,999		288,803		(21,730)			(44,734)
Beginning balance (Accounting Standards Update 2016-13) at Dec. 31, 2019		$ (11,047)		$ 0		$ 0		$ (11,284)		$ 237	[1]		$ 0
Beginning balance, shares at Dec. 31, 2019			29,334,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,923		$ 0		0		2,923		0			0
Other comprehensive income, net of income tax	1,686		0		0		0		1,686			0
Cash dividends declared	(11,677)		0		0		(11,677)		0			0
Stock-based compensation	1,061		0		1,075		(14)		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	1,163		$ 0		(111)		0		0			1,274
Stock issued under dividend reinvestment and employee stock purchase plans, shares			64,154
Vesting of restricted stock unit awards	0		$ 0		(346)		0		0			346
Vesting of restricted stock unit awards, shares			17,035
Exercise of stock options	$ 94		$ 0		(7)		0		0			101
Exercise of stock options, shares	5,000		5,000
Cancellations of performance-based restricted stock awards	$ 0		$ 0		418		0		0			(418)
Cancellation of performance-based restricted stock awards, shares			(14,777)
Purchases of treasury stock	(4,452)		$ 0		0		0		0			(4,452)
Purchases of treasury stock, shares			(204,056)
Ending balance at Jun. 30, 2020	$ 654,873		$ 157,784		296,028		268,751		(19,807)			(47,883)
Ending balance, shares at Jun. 30, 2020			29,201,985
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.40
Beginning balance at Mar. 31, 2020	$ 651,551		$ 157,784		295,439		272,478		(25,628)			(48,522)
Beginning balance, shares at Mar. 31, 2020			29,164,782
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,085		$ 0		0		2,085		0			0
Other comprehensive income, net of income tax	5,821		0		0		0		5,821			0
Cash dividends declared	(5,811)		0		0		(5,811)		0			0
Stock-based compensation	650		0		651		(1)		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	591		$ 0		(62)		0		0			653
Stock issued under dividend reinvestment and employee stock purchase plans, shares			38,109
Purchases of treasury stock	(14)		$ 0		0		0		0			(14)
Purchases of treasury stock, shares			(906)
Ending balance at Jun. 30, 2020	$ 654,873		$ 157,784		$ 296,028		$ 268,751		$ (19,807)			$ (47,883)
Ending balance, shares at Jun. 30, 2020			29,201,985
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.20

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2020" for additional information.