Condensed 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, 2017	$ 505,808	$ 255,836	$ 255,200	$ (5,228)
Beginning balance, shares at Dec. 31, 2017		22,955,963
Net income	28,939		28,939
Adoption ASU | ASU 2016-01 [Member]			(62)	62
Adoption ASU | ASU 2018-02 [Member]			1,093	(1,093)
Other comprehensive income (loss)	(14,864)			(14,864)
Stock option vesting	54	$ 54
Stock options exercised	223	$ 223
Stock options exercised, shares		14,500
RSU vesting	471	$ 471
PSU vesting, value	197	$ 197
RSUs released, shares		25,398
PSUs released, shares		25,512
Repurchase of common stock, value	(671)	$ (191)	(480)
Repurchase of common stock, shares		(17,220)
Dividends paid	(7,813)		(7,813)
Ending balance at Jun. 30, 2018	512,344	$ 256,590	276,877	(21,123)
Ending balance, shares at Jun. 30, 2018		23,004,153
Beginning balance at Mar. 31, 2018	505,256	$ 256,226	266,235	(17,205)
Beginning balance, shares at Mar. 31, 2018		22,956,323
Net income	15,029		15,029
Other comprehensive income (loss)	(3,918)			(3,918)
Stock option vesting	17	$ 17
Stock options exercised	223	$ 223
Stock options exercised, shares		14,500
RSU vesting	233	$ 233
PSU vesting, value	81	$ 81
RSUs released, shares		24,904
PSUs released, shares		25,512
Repurchase of common stock, value	(667)	$ (190)	(477)
Repurchase of common stock, shares		(17,086)
Dividends paid	(3,910)		(3,910)
Ending balance at Jun. 30, 2018	512,344	$ 256,590	276,877	(21,123)
Ending balance, shares at Jun. 30, 2018		23,004,153
Beginning balance at Dec. 31, 2018	$ 827,373	$ 541,762	303,490	(17,879)
Beginning balance, shares at Dec. 31, 2018	30,417,223	30,417,223
Net income	$ 45,787		45,787
Other comprehensive income (loss)	15,681			15,681
Stock option vesting	0
Stock options exercised	$ 2,500	$ 2,500
Stock options exercised, shares	157,000	157,000
RSU vesting	$ 567	$ 567
PSU vesting, value	248	$ 248
RSUs released, shares		26,211
PSUs released, shares		22,237
Repurchase of common stock, value	(4,695)	$ (2,138)	(2,557)
Repurchase of common stock, shares		(119,914)
Dividends paid	(11,575)		(11,575)
Ending balance at Jun. 30, 2019	$ 875,886	$ 542,939	335,145	(2,198)
Ending balance, shares at Jun. 30, 2019	30,502,757	30,502,757
Beginning balance at Mar. 31, 2019	$ 853,278	$ 542,340	319,865	(8,927)
Beginning balance, shares at Mar. 31, 2019		30,432,419
Net income	23,061		23,061
Other comprehensive income (loss)	6,729			6,729
Stock option vesting	0
Stock options exercised	1,853	$ 1,853
Stock options exercised, shares		116,000
RSU vesting	289	$ 289
PSU vesting, value	129	$ 129
RSUs released, shares		25,856
PSUs released, shares		22,237
Repurchase of common stock, value	(3,660)	$ (1,672)	(1,988)
Repurchase of common stock, shares		(93,755)
Dividends paid	(5,793)		(5,793)
Ending balance at Jun. 30, 2019	$ 875,886	$ 542,939	$ 335,145	$ (2,198)
Ending balance, shares at Jun. 30, 2019	30,502,757	30,502,757