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				$ 0		$ 0				$ 237		$ 0
Beginning balance (Accounting Standards Update 2016-02) at Dec. 31, 2019		$ (11,047)						$ (11,284)
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 units, net of shares withheld to cover income taxes	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 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
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	53,478		$ 0		0		53,478		0		0
Other comprehensive income, net of income tax	2,599		0		0		0		2,599		0
Cash dividends declared	(11,741)		0		0		(11,741)		0		0
Stock-based compensation	1,643		0		1,700		(56)		0		(1)
Stock issued under dividend reinvestment and employee stock purchase plans	1,214		$ 0		90		(1)		0		1,125
Stock issued under dividend reinvestment and employee stock purchase plans, shares			45,226
Vesting of restricted stock units, net of shares withheld to cover income taxes	(355)		$ 0		(1,126)		0		0		771
Vesting of restricted stock unit awards, shares			42,619
Exercise of stock options	$ 983		$ 0		31		0		0		952
Shares under option, exercised	(46,527)		(46,527)
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 Jun. 30, 2021	$ 739,998		$ 157,784		297,208		348,579		(19,545)		(44,028)
Ending balance, shares at Jun. 30, 2021			29,411,731
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.40
Beginning balance at Mar. 31, 2021	$ 722,455		$ 157,784		296,177		333,581		(20,440)		(44,647)
Beginning balance, shares at Mar. 31, 2021			29,379,575
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,875		$ 0		0		20,875		0		0
Other comprehensive income, net of income tax	895		0		0		0		895		0
Cash dividends declared	(5,877)		0		0		(5,877)		0		0
Stock-based compensation	821		0		822		0		0		(1)
Stock issued under dividend reinvestment and employee stock purchase plans	605		$ 0		25		0		0		580
Stock issued under dividend reinvestment and employee stock purchase plans, shares			21,915
Exercise of stock options	224		$ 0		14		0		0		210
Shares under option, exercised			(10,241)
Cancellation of performance-based restricted stock awards	0		$ 0		(170)		0		0		(170)
Cancellation of performance-based restricted stock awards, shares			0
Ending balance at Jun. 30, 2021	$ 739,998		$ 157,784		$ 297,208		$ 348,579		$ (19,545)		$ (44,028)
Ending balance, shares at Jun. 30, 2021			29,411,731
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.20