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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (6,920)	[1]	$ (6,101)
Net Change	(5,530)	692	(6,309)		206
Ending balance	(13,229)	(5,895)	(13,229)		(5,895)
Net Unrealized Gains on Available-for-Sale Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			8,344		7,306
Net Change			(7,884)		159
Ending balance	460	7,465	460		7,465
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		(253)
Ending balance		(1,185)			(1,185)
Net Change Related to Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(14,023)		(12,475)
Net Change			334		300
Ending balance	$ (13,689)	$ (12,175)	$ (13,689)		$ (12,175)

[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.