Consolidated Statements Of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Dec. 31, 2016		15,476,379
Beginning Balance at Dec. 31, 2016	$ 391,547	$ 156,041	$ 249,415	$ (13,909)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of certain income tax effects from AOCI —ASU 2018-02 (Note 15)			3,476	(3,476)
Net income	28,476		28,476
Other comprehensive loss, net of tax	(2,829)			(2,829)
Stock-based compensation expense	1,469	$ 1,469
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit		48,325
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit	(606)	$ (606)
Cash dividends declared ( $1.23, $1.15 and $0.94 per share in 2019, 2018, and 2017, respectively)	(14,644)		(14,644)
Ending Balance (in shares) at Dec. 31, 2017		15,524,704
Ending Balance at Dec. 31, 2017	403,413	$ 156,904	266,723	(20,214)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,071		53,071
Other comprehensive loss, 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		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 ( $1.23, $1.15 and $0.94 per share in 2019, 2018, and 2017, respectively)	(17,962)		(17,962)
Ending Balance (in shares) at Dec. 31, 2018		15,591,914.000
Ending Balance at Dec. 31, 2018	435,825	$ 158,215	302,030	(24,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	57,203
Other comprehensive loss, 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		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 ( $1.23, $1.15 and $0.94 per share in 2019, 2018, and 2017, respectively)	(18,907)		(18,907)
Ending Balance (in shares) at Dec. 31, 2019		15,144,719.000
Ending Balance at Dec. 31, 2019	$ 473,415	$ 139,103	$ 340,580	$ (6,268)