Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 12,315	$ 13,241	$ 12,262
Other Comprehensive Income (Loss)
Net unrealized holding gain (loss) on securities available for sale	3,112	(3,258)	(1,174)
Reclassification adjustment for realized gains included in net income	(708)	(1,023)	(436)
Net unrealized gain (loss) on derivative used for cash flow hedges		1	108
Net unrealized gain (loss) relating to defined benefit plan	(20)	62	77
Other comprehensive income, before tax, total	2,384	(4,218)	(1,425)
Income tax benefit (expense) related to other comprehensive income	(749)	1,474	537
Other comprehensive income (loss), net of tax	1,635	(2,744)	(888)
Comprehensive Income	$ 13,950	$ 10,497	$ 11,374