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	50,209		$ 0		0		50,209		0			0
Other comprehensive income, net of income tax	6,325		0		0		0		6,325			0
Cash dividends declared	(17,572)		0		0		(17,572)		0			0
Stock-based compensation	1,870		0		1,870		0		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	1,669		$ 0		114		1		0			1,554
Stock issued under dividend reinvestment and employee stock purchase plans, shares			69,126
Exercise of stock options	1,005		$ 0		(170)		0		0			1,175
Exercise of stock options, shares			58,545
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	(1,776)		$ 0		0		0		0			(1,776)
Purchases of treasury stock, shares			(68,640)
Ending balance at Sep. 30, 2019	$ 664,299		$ 157,784		294,556		279,158		(22,008)			(45,191)
Ending balance, shares at Sep. 30, 2019			29,312,534
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.60
Beginning balance at Jun. 30, 2019	$ 651,670		$ 157,784		293,947		267,357		(21,949)			(45,469)
Beginning balance, shares at Jun. 30, 2019			29,294,942
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,662		$ 0		0		17,662		0			0
Other comprehensive income, net of income tax	(59)		0		0		0		(59)			0
Cash dividends declared	(5,861)		0		0		(5,861)		0			0
Stock-based compensation	640		0		640		0		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	534		$ 0		37		0		0			497
Stock issued under dividend reinvestment and employee stock purchase plans, shares			20,943
Exercise of stock options	314		$ 0		(68)		0		0			382
Exercise of stock options, shares			19,045
Purchases of treasury stock	(601)		$ 0		0		0		0			(601)
Purchases of treasury stock, shares			(22,396)
Ending balance at Sep. 30, 2019	$ 664,299		$ 157,784		294,556		279,158		(22,008)			(45,191)
Ending balance, shares at Sep. 30, 2019			29,312,534
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	21,042		$ 0		0		21,042		0			0
Other comprehensive income, net of income tax	2,393		0		0		0		2,393			0
Cash dividends declared	(17,522)		0		0		(17,522)		0			0
Stock-based compensation	1,720		0		1,733		(13)		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	1,757		$ 0		(198)		0		0			1,955
Stock issued under dividend reinvestment and employee stock purchase plans, shares			103,471
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 Sep. 30, 2020	$ 669,107		$ 157,784		296,599		281,026		(19,100)			(47,202)
Ending balance, shares at Sep. 30, 2020			29,241,302
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.60
Beginning balance at Jun. 30, 2020	$ 654,873		$ 157,784		296,028		268,751		(19,807)			(47,883)
Beginning balance, shares at Jun. 30, 2020			29,201,985
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,119		$ 0		0		18,119		0			0
Other comprehensive income, net of income tax	707		0		0		0		707			0
Cash dividends declared	(5,845)		0		0		(5,845)		0			0
Stock-based compensation	659		0		658		1		0			0
Stock issued under dividend reinvestment and employee stock purchase plans	594		$ 0		(87)		0		0			681
Stock issued under dividend reinvestment and employee stock purchase plans, shares			39,317
Ending balance at Sep. 30, 2020	$ 669,107		$ 157,784		$ 296,599		$ 281,026		$ (19,100)			$ (47,202)
Ending balance, shares at Sep. 30, 2020			29,241,302
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.