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, 2015	[1]		15,330,717
Beginning Balance at Dec. 31, 2015		$ 363,190	$ 153,083	$ 222,329	$ (12,222)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Stock Splits	[2]		(173)
Stockholders' Equity Note, Stock Split, Reduction of Capital	[2]	(5)	$ (5)
Net Income		29,165		29,165
Other comprehensive income, net of tax		8,047			8,047
Stock-based compensation expense		1,521	$ 1,521
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)	[1]		104,312
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings		593	$ 593
Cash dividends declared ($0.40 and $0.46 per share in six months ended June 30, 2016 and June 30, 2017)	[1]	(9,330)		(9,330)
Ending Balance (in shares) at Sep. 30, 2016	[1]		15,434,856
Ending Balance at Sep. 30, 2016		393,181	$ 155,264	242,092	(4,175)
Beginning Balance (in shares) at Dec. 31, 2015	[1]		15,330,717
Beginning Balance at Dec. 31, 2015		363,190	$ 153,083	222,329	(12,222)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment(2)	[3]	0	$ 72	(72)
Ending Balance (in shares) at Dec. 31, 2016	[1]		15,476,379
Ending Balance at Dec. 31, 2016		391,547	$ 156,041	249,415	(13,909)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		31,649
Other comprehensive income, net of tax		1,398			1,398
Stock-based compensation expense		1,135	$ 1,135
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings and tax benefit (shares)	[1]		39,198
Exercise of stock options and issuance of vested share awards, net of repurchase for tax withholdings		(615)	$ (615)
Cash dividends declared ($0.40 and $0.46 per share in six months ended June 30, 2016 and June 30, 2017)	[1]	(10,748)		(10,748)
Ending Balance (in shares) at Sep. 30, 2017	[1]		15,515,577.000
Ending Balance at Sep. 30, 2017		$ 414,366	$ 156,561	$ 270,316	$ (12,511)

[1] (1) Share and per share amounts as of December 31, 2015 have been adjusted to reflect the three-for-two stock split effective September 30, 2016.

[2] (3)In the third quarter of 2016, the Company paid shareholders cash in-lieu of fractional shares of common stock in connection with the three-for-two stock split effective September 30, 2016.

[3] (2)In the second quarter of 2016, the Company adopted ASU 2016-09, effective January 1, 2016. The Company made a policy election to not estimate the forfeiture rate in the accounting for share-based compensation on its unvested share-based awards. The change in policy was accounted for on a modified-retrospective basis and represents the cumulative effect adjustment to shareholders' equity.