Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 5,026	$ 4,771	$ 9,502	$ 8,579
Unrealized (losses) gains on securities:
Unrealized holding (losses) gains arising during period	(18,656)	824	(20,889)	2,708
Less: reclassification adjustment for gains included in net income	(781)	(442)	(1,664)	(590)
Total unrealized (losses) gains on securities	(19,437)	382	(22,553)	2,118
Defined benefit pension plans:
Amortization of prior service cost and loss included in net periodic benefit cost	174	162	347	324
Other comprehensive (loss) income	(19,263)	544	(22,206)	2,442
Comprehensive (loss) income	$ (14,237)	$ 5,315	$ (12,704)	$ 11,021