Consolidated Statements Of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance (in shares) at Dec. 31, 2017			15,524,704
Beginning Balance at Dec. 31, 2017	$ 403,413		$ 156,904	$ 266,723		$ (20,214)
Beginning Balance (ASU 2016-01) at Dec. 31, 2017					$ 198		$ (198)
Beginning Balance (ASU 2017-12) at Dec. 31, 2017		$ 665					$ 665
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,071			53,071
Other comprehensive income, net of tax	(4,673)					(4,673)
Stock-based compensation expense	1,688		$ 1,688
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)			67,960
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit	(350)		$ (350)
Common stock repurchased (in shares)			(750)
Common stock repurchased	(27)		$ (27)
Cash dividends declared ( $1.32, $1.23 and $1.15 per share in 2020, 2019, and 2018, respectively)	(17,962)			(17,962)
Ending Balance (in shares) at Dec. 31, 2018			15,591,914
Ending Balance at Dec. 31, 2018	$ 435,825	254	$ 158,215	302,030	254	(24,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Net income	$ 57,203			57,203
Other comprehensive income, net of tax	18,152					18,152
Stock-based compensation expense	1,885		$ 1,885
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)			40,857
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit	(202)		$ (202)
Common stock repurchased (in shares)			(488,052)
Common stock repurchased	(20,795)		$ (20,795)
Cash dividends declared ( $1.32, $1.23 and $1.15 per share in 2020, 2019, and 2018, respectively)	(18,907)			(18,907)
Ending Balance (in shares) at Dec. 31, 2019			15,144,719
Ending Balance at Dec. 31, 2019	$ 473,415	$ (2,809)	$ 139,103	340,580	$ (2,809)	(6,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Net income	$ 59,486			59,486
Other comprehensive income, net of tax	27,008					27,008
Stock-based compensation expense	1,785		$ 1,785
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)			38,732
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit	(116)		$ (116)
Common stock repurchased (in shares)			(274,354)
Common stock repurchased	(9,700)		$ (9,700)
Cash dividends declared ( $1.32, $1.23 and $1.15 per share in 2020, 2019, and 2018, respectively)	(19,755)			(19,755)
Ending Balance (in shares) at Dec. 31, 2020			14,909,097
Ending Balance at Dec. 31, 2020	$ 529,314		$ 131,072	$ 377,502		$ 20,740