Components of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gain (loss) on securities available-for-sale	$ 8,616	$ 6,669
Net unrealized loss on securities available-for-sale for which a portion of an other-than-temporary impairment has been recognized in income	(3,745)	(3,791)
Net unrealized loss on derivative used for cash flow hedges	(416)	(472)
Net unrealized loss relating to defined benefit plan liability	(49)	(448)
Accumulated other comprehensive income loss before tax	4,406	1,958
Tax expense (benefit)	1,603	755
Net of tax amount	$ 2,803	$ 1,203