Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2014	$ 418,172	$ 244,318	$ 176,057	$ (2,203)
Beginning balance, shares at Dec. 31, 2014		22,714,964
Net income	43,818		43,818
Other comprehensive income (loss)	425			425
Stock option vesting	734	$ 734
RSU vesting	457	457
PSU vesting	179	179
Stock options exercised	3,116	$ 3,116
Stock options exercised, shares		154,500
Tax effect of stock options exercised	(83)	$ (83)
RSUs released	0	$ 0	0	0
RSUs released, shares		12,064
Tax benefit from release of RSUs	15	$ 15
Repurchase of common stock, value	(2,868)	$ (1,149)	(1,719)
Repurchase of common stock, shares		(106,355)
Dividends paid	(11,849)		(11,849)
Ending balance at Dec. 31, 2015	452,116	$ 247,587	206,307	(1,778)
Ending balance, shares at Dec. 31, 2015		22,775,173
Net income	44,811		44,811
Other comprehensive income (loss)	(6,135)			(6,135)
Stock option vesting	580	$ 580
RSU vesting	616	616
PSU vesting	271	271
Stock options exercised	6,506	$ 6,506
Stock options exercised, shares		336,900
Tax effect of stock options exercised	154	$ 154
RSUs released	0	$ 0	0	0
RSUs released, shares		20,529
Tax benefit from release of RSUs	1	$ 1
Repurchase of common stock, value	(7,878)	$ (2,895)	(4,983)
Repurchase of common stock, shares		(264,800)
Dividends paid	(13,695)		(13,695)
Ending balance at Dec. 31, 2016	$ 477,347	$ 252,820	232,440	(7,913)
Ending balance, shares at Dec. 31, 2016	22,867,802	22,867,802
Net income	$ 40,554		40,554
Other comprehensive income (loss)	2,685			2,685
Stock option vesting	259	$ 259
RSU vesting	895	895
PSU vesting	432	432
Stock options exercised	$ 2,621	$ 2,621
Stock options exercised, shares	145,850	145,850
RSUs released	$ 0	$ 0	0	0
RSUs released, shares		30,896
PSUs released	0	$ 0	0	0
PSUs released, shares		18,805
Repurchase of common stock, value	(3,854)	$ (1,191)	(2,663)
Repurchase of common stock, shares		(107,390)
Dividends paid	(15,131)		(15,131)
Ending balance at Dec. 31, 2017	$ 505,808	$ 255,836	$ 255,200	$ (5,228)
Ending balance, shares at Dec. 31, 2017	22,955,963	22,955,963