Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income Component Details (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Securities available-for-sale:
Net securities gains reclassified into earnings	$ (113)	$ (985)	$ (129)	$ (1,085)
Related income tax expense	42	366	47	403
Net effect on accumulated other comprehensive income for the period	(71)	(619)	(82)	(682)
Securities held-to-maturity:
Amortization of unrealized gain transferred from available-for-sale	(362)	(403)	(650)	(829)
Related income tax expense	133	149	244	317
Net effect on accumulated other comprehensive income for the period	(229)	(254)	(406)	(512)
Defined benefit pension plan :
Amortization of net loss and prior service costs	909	580	1,743	1,160
Related income tax expense	(334)	(215)	(693)	(486)
Net effect on accumulated other comprehensive income for the period	575	365	1,050	674
Total reclassifications for the period	$ 275	$ (508)	$ 562	$ (520)