Accumulated Other Comprehensive (Loss) Income - Amounts Reclassified Out of Each Component of Accumulated Comprehensive (Loss) Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on sales of investment securities	$ 1,426	$ 9	$ 2,950	$ 291
Amortization of net loss included in net periodic pension costs	320	293	961	882
Other-than-temporary impairment on equity securities		(4)		(13)
Accretion of prior service cost included in net periodic pension costs	(64)	(64)	(191)	(192)
Income before income taxes	7,439	7,612	20,914	19,989
Tax expense (benefit)	(1,400)	(1,842)	(4,647)	(4,193)
Net of tax	6,039	5,770	16,267	15,796
Amount Reclassified from Accumulated Other Comprehensive (Loss) Income [Member] | Net Unrealized Holding Gains (Losses) on Available-for-Sale Investment Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on sales of investment securities	1,426	9	2,950	291
Other-than-temporary impairment on equity securities		(4)		(13)
Income before income taxes	1,426	5	2,950	278
Tax expense (benefit)	(499)	(1)	(1,032)	(97)
Net of tax	927	4	1,918	181
Amount Reclassified from Accumulated Other Comprehensive (Loss) Income [Member] | Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net loss on interest rate swap			(1,866)
Income before income taxes			(1,866)
Tax expense (benefit)			653
Net of tax			(1,213)
Amount Reclassified from Accumulated Other Comprehensive (Loss) Income [Member] | Net Change Related to Defined Benefit Pension Plan [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net loss included in net periodic pension costs	(320)	(293)	(961)	(882)
Accretion of prior service cost included in net periodic pension costs	64	64	191	192
Income before income taxes	(256)	(229)	(770)	(690)
Tax expense (benefit)	90	81	270	242
Net of tax	$ (166)	$ (148)	$ (500)	$ (448)