Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive (Loss) Income, Net of Taxes (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (6,920)	[1]	$ (6,101)
Net Change	(474)	1,760	(6,783)		1,966
Ending balance	(13,703)	(4,135)	(13,703)		(4,135)
Net Unrealized Holding Gains (Losses) on Available-for-Sale Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			8,344		7,306
Net Change			(8,524)		1,909
Ending balance	(180)	9,215	(180)		9,215
Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(1,241)		(932)
Net Change			1,241		(391)
Ending balance		(1,323)			(1,323)
Net Change Related to Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(14,023)		(12,475)
Net Change			500		448
Ending balance	$ (13,523)	$ (12,027)	$ (13,523)		$ (12,027)

[1] Note: The consolidated balance sheet at December 31, 2012 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U. S. generally accepted accounting principles for complete financial statements. See accompanying notes to the unaudited consolidated financial statements.