Components of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gain on securities available-for-sale	$ 7,861	$ 8,616
Net unrealized loss on securities available-for-sale for which a portion of other-than-temporary impairment has been recognized in income	(4,279)	(3,745)
Net unrealized loss on derivative used for cash flow hedges	(379)	(416)
Net unrealized loss relating to defined benefit plan liability	(49)	(49)
Accumulated other comprehensive income loss before tax	3,154	4,406
Tax expense	1,165	1,603
Net-of-tax amount	$ 1,989	$ 2,803