Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Treasury Stock [Member]
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			74,389
Other comprehensive income, net of income tax	2,071				2,071
Cash dividends declared	(17,624)			(17,624)
Stock-based compensation	2,496		2,552	(56)		0
Stock issued under dividend reinvestment and employee stock purchase plans	(1,824)		(90)	(1)		(1,735)
Stock issued under dividend reinvestment and employee stock purchase plans, shares		67,553
Vesting of restricted stock units, net of shares withheld to cover taxes	(355)		(1,153)			798
Vesting of restricted stock unit awards, shares		43,963
Exercise of stock options	1,045		31			1,014
Shares under option, exercised		49,527
Cancellation of performance-based restricted stock awards			327			(327)
Cancellation of performance-based restricted stock awards, shares		(7,199)
Purchases of treasury stock	(295)					(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			20,911
Other comprehensive income, net of income tax	(528)				(528)
Cash dividends declared	(5,883)			(5,883)
Stock-based compensation	853		852			1
Stock issued under dividend reinvestment and employee stock purchase plans	(610)		0			(610)
Stock issued under dividend reinvestment and employee stock purchase plans, shares		22,327
Vesting of restricted stock units, net of shares withheld to cover taxes	0	$ 0	(27)	0	0	27
Vesting of restricted stock unit awards, shares		1,344
Exercise of stock options	62		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
Beginning balance at Dec. 31, 2021	$ 773,794	$ 157,784	299,181	375,124	(16,353)	(41,942)
Beginning balance, shares at Dec. 31, 2021		29,500,542
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54,284			54,284
Other comprehensive income, net of income tax	(48,632)				(48,632)
Cash dividends declared	(18,258)			(18,258)
Stock-based compensation	2,774		2,982	(208)
Stock issued under dividend reinvestment and employee stock purchase plans	(1,934)		(129)			(1,805)
Stock issued under dividend reinvestment and employee stock purchase plans, shares		74,055
Vesting of restricted stock units, net of shares withheld to cover taxes	(903)		(2,551)			1,648
Vesting of restricted stock unit awards, shares		92,073
Exercise of stock options	$ 575		50			525
Shares under option, exercised	25,781	25,781
Purchases of treasury stock	$ (11,381)					(11,381)
Purchases of treasury stock, shares		(450,000)
Ending balance at Sep. 30, 2022	$ 754,187	$ 157,784	299,791	410,942	(64,985)	(49,345)
Ending balance, shares at Sep. 30, 2022		29,242,451
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.62
Beginning balance at Jun. 30, 2022	$ 763,925	$ 157,784	298,800	396,295	(42,781)	(46,173)
Beginning balance, shares at Jun. 30, 2022		29,365,775
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,801			20,801
Other comprehensive income, net of income tax	(22,204)				(22,204)
Cash dividends declared	(6,153)			(6,153)
Stock-based compensation	972		973	(1)
Stock issued under dividend reinvestment and employee stock purchase plans	(659)		(25)			(634)
Stock issued under dividend reinvestment and employee stock purchase plans, shares		26,438
Vesting of restricted stock units, net of shares withheld to cover taxes	(2)		(7)			5
Vesting of restricted stock unit awards, shares		238
Purchases of treasury stock	(3,811)					(3,811)
Purchases of treasury stock, shares		(150,000)
Ending balance at Sep. 30, 2022	$ 754,187	$ 157,784	$ 299,791	$ 410,942	$ (64,985)	$ (49,345)
Ending balance, shares at Sep. 30, 2022		29,242,451
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared, per share	$ 0.21