Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 3,604	$ 2,694	$ 2,557	$ 1,963	$ 2,640	$ 2,472	$ 2,112	$ 1,976	$ 2,003	$ 2,173	$ 1,644	$ 1,426	$ 10,818	$ 9,200	$ 7,246
Other comprehensive income:
Net unrealized holding gain (loss) on securities available-for-sale													8,921	(9,810)	4,782
Net unrealized gain (loss) on securities available-for-sale for which a portion of an other-than-temporary impairment has been recognized in income													381	800	43
Reclassification adjustment for realized gains included in net income													(313)	(835)	(2,831)
Net unrealized gain on derivative used for cash flow hedges													150	157	56
Net unrealized gain (loss) relating to defined benefit plan													(209)	149	399
Other Comprehensive Income (Loss), before Tax, Total													8,930	(9,539)	2,449
Income tax (expense) benefit related to other comprehensive income													(3,137)	3,321	(849)
Other comprehensive income (loss)													5,793	(6,218)	1,600
Comprehensive income (Loss)													$ 16,611	$ 2,982	$ 8,846