CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - 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]
Net Income	10,076		10,076
Other comprehensive income, net of tax	(29)			(29)
Stock-based compensation expense	366	$ 366
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)		31,646
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings	(552)	$ (552)
Cash dividends declared ($0.23 and $0.25 per share	(3,581)		(3,581)
Ending Balance (in shares) at Mar. 31, 2017		15,508,025
Ending Balance at Mar. 31, 2017	397,827	$ 155,855	255,910	(13,938)
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	12,820
Other comprehensive income, net of tax	(8,234)			(8,234)
Stock-based compensation expense	431	$ 431
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)		41,164
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings	(475)	$ (475)
Cash dividends declared ($0.23 and $0.25 per share	(3,900)		(3,900)
Ending Balance (in shares) at Mar. 31, 2018		15,565,868.000
Ending Balance at Mar. 31, 2018	$ 404,055	$ 156,860	275,841	(28,646)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment (Note 2)			$ 198	$ (198)