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, 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		$ 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 units	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
Shares under option, exercised			5,000
Cancellation 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
Beginning balance at Dec. 31, 2020	$ 692,472		$ 157,784		296,186		306,899		(22,144)		(46,253)
Beginning balance, shares at Dec. 31, 2020			29,295,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,389		$ 0		0		74,389		0		0
Other comprehensive income, net of income tax	2,071		0		0		0		2,071		0
Cash dividends declared	(17,624)		0		0		(17,624)		0		0
Stock-based compensation	2,496		0		2,552		(56)		0		0
Stock issued under dividend reinvestment and employee stock purchase plans	1,824		$ 0		90		(1)		0		1,735
Stock issued under dividend reinvestment and employee stock purchase plans, shares			67,553
Vesting of restricted stock units	(355)		$ 0		(1,153)		0		0		798
Vesting of restricted stock unit awards, shares			43,963
Exercise of stock options	$ 1,045		$ 0		31		0		0		1,014
Shares under option, exercised	(49,527)		(49,527)
Cancellation of performance-based restricted stock awards	$ 0		$ 0		327		0		0		(327)
Cancellation of performance-based restricted stock awards, shares			(7,199)
Purchases of treasury stock	(295)		$ 0		0		0		0		(295)
Purchases of treasury stock, shares			(10,494)
Ending balance at Sep. 30, 2021	$ 756,023		$ 157,784		298,033		363,607		(20,073)		(43,328)
Ending balance, shares at Sep. 30, 2021			29,438,402
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.60
Beginning balance at Jun. 30, 2021	$ 739,998		$ 157,784		297,208		348,579		(19,545)		(44,028)
Beginning balance, shares at Jun. 30, 2021			29,411,731
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,911		$ 0		0		20,911		0		0
Other comprehensive income, net of income tax	(528)		0		0		0		(528)		0
Cash dividends declared	(5,883)		0		0		(5,883)		0		0
Stock-based compensation	853		0		852		0		0		1
Stock issued under dividend reinvestment and employee stock purchase plans	610		$ 0		0		0		0		610
Stock issued under dividend reinvestment and employee stock purchase plans, shares			22,327
Vesting of restricted stock units	0		$ 0		(27)		0		0		27
Vesting of restricted stock unit awards, shares			1,344
Exercise of stock options	62		$ 0		0		0		0		62
Shares under option, exercised			(3,000)
Ending balance at Sep. 30, 2021	$ 756,023		$ 157,784		$ 298,033		$ 363,607		$ (20,073)		$ (43,328)
Ending balance, shares at Sep. 30, 2021			29,438,402
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.20