Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive (Loss) Income, Net of Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	$ (9,955)	$ (6,920)	$ (6,101)
Net Change	(4,507)	(3,035)	(819)
Ending balance	(14,462)	(9,955)	(6,920)
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	(1,472)	8,344	7,306
Net Change	3,183	(9,816)	1,038
Ending balance	1,711	(1,472)	8,344
Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	0	(1,241)	(932)
Net Change	(157)	1,241	(309)
Ending balance	(157)	0	(1,241)
Net Change Related to Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	(8,483)	(14,023)	(12,475)
Net Change	(7,533)	5,540	(1,548)
Ending balance	$ (16,016)	$ (8,483)	$ (14,023)