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, 2016	$ 477,347	$ 252,820	$ 232,440	$ (7,913)
Beginning balance, shares at Dec. 31, 2016		22,867,802
Net income	12,079		12,079
Other comprehensive income (loss)	511			511
Stock option vesting	88	$ 88
RSU vesting	204	204
PSU vesting	89	89
Stock options exercised	435	$ 435
Stock options exercised, shares		21,450
RSUs released	0	$ 0	0	0
RSUs released, shares		304
Repurchase of common stock, value	(604)	$ (180)	(424)
Repurchase of common stock, shares		(16,251)
Dividends paid	(3,431)		(3,431)
Ending balance at Mar. 31, 2017	486,718	$ 253,456	240,664	(7,402)
Ending balance, shares at Mar. 31, 2017		22,873,305
Beginning balance at Dec. 31, 2017	$ 505,808	$ 255,836	255,200	(5,228)
Beginning balance, shares at Dec. 31, 2017	22,955,963	22,955,963
Net income	$ 13,910		13,910
Adoption ASU | ASU 2016-01 [Member]			(62)	62
Adoption ASU | ASU 2018-02 [Member]			1,093	(1,093)
Other comprehensive income (loss)	(10,946)			(10,946)
Stock option vesting	37	$ 37
RSU vesting	238	238
PSU vesting	$ 116	116
Stock options exercised, shares	0
RSUs released	$ 0	$ 0	0	0
RSUs released, shares		494
Repurchase of common stock, value	(4)	$ (1)	(3)
Repurchase of common stock, shares		(134)
Dividends paid	(3,903)		(3,903)
Ending balance at Mar. 31, 2018	$ 505,256	$ 256,226	$ 266,235	$ (17,205)
Ending balance, shares at Mar. 31, 2018	22,956,323	22,956,323